diff --git a/.waf-tools/default-compiler-flags.py b/.waf-tools/default-compiler-flags.py
index e690290..9e045c3 100644
--- a/.waf-tools/default-compiler-flags.py
+++ b/.waf-tools/default-compiler-flags.py
@@ -20,9 +20,9 @@
                       'The minimum supported gcc version is 5.3.0.')
         conf.flags = GccFlags()
     elif cxx == 'clang':
-        if ccver < (3, 5, 0):
+        if ccver < (3, 6, 0):
             errmsg = ('The version of clang you are using is too old.\n'
-                      'The minimum supported clang version is 3.5.0.')
+                      'The minimum supported clang version is 3.6.0.')
         conf.flags = ClangFlags()
     else:
         warnmsg = 'Note: %s compiler is unsupported' % cxx
@@ -129,6 +129,10 @@
     def getGeneralFlags(self, conf):
         flags = super(GccBasicFlags, self).getGeneralFlags(conf)
         flags['CXXFLAGS'] += ['-std=c++14']
+        if Utils.unversioned_sys_platform() == 'linux':
+            flags['LINKFLAGS'] += ['-fuse-ld=gold']
+        elif Utils.unversioned_sys_platform() == 'freebsd':
+            flags['LINKFLAGS'] += ['-fuse-ld=lld']
         return flags
 
     def getDebugFlags(self, conf):
@@ -145,7 +149,7 @@
                               '-Wno-error=maybe-uninitialized', # Bug #1615
                               '-Wno-unused-parameter',
                               ]
-        flags['LINKFLAGS'] += ['-fuse-ld=gold', '-Wl,-O1']
+        flags['LINKFLAGS'] += ['-Wl,-O1']
         return flags
 
     def getOptimizedFlags(self, conf):
@@ -158,7 +162,7 @@
                               '-Wnon-virtual-dtor',
                               '-Wno-unused-parameter',
                               ]
-        flags['LINKFLAGS'] += ['-fuse-ld=gold', '-Wl,-O1']
+        flags['LINKFLAGS'] += ['-Wl,-O1']
         return flags
 
 class GccFlags(GccBasicFlags):
@@ -179,6 +183,8 @@
             # Bug #4296
             flags['CXXFLAGS'] += [['-isystem', '/usr/local/include'], # for Homebrew
                                   ['-isystem', '/opt/local/include']] # for MacPorts
+        if Utils.unversioned_sys_platform() == 'freebsd':
+            flags['CXXFLAGS'] += [['-isystem', '/usr/local/include']] # Bug #4790
         return flags
 
     def getDebugFlags(self, conf):
@@ -186,15 +192,13 @@
         flags['CXXFLAGS'] += ['-fcolor-diagnostics',
                               '-Wextra-semi',
                               '-Wundefined-func-template',
-                              '-Wno-error=deprecated-register',
-                              '-Wno-error=infinite-recursion', # Bug #3358
-                              '-Wno-error=keyword-macro', # Bug #3235
-                              '-Wno-error=unneeded-internal-declaration', # Bug #1588
                               '-Wno-unused-local-typedef', # Bugs #2657 and #3209
                               ]
         version = self.getCompilerVersion(conf)
         if version < (3, 9, 0) or (Utils.unversioned_sys_platform() == 'darwin' and version < (8, 1, 0)):
             flags['CXXFLAGS'] += ['-Wno-unknown-pragmas']
+        if version < (6, 0, 0):
+            flags['CXXFLAGS'] += ['-Wno-missing-braces'] # Bug #4721
         return flags
 
     def getOptimizedFlags(self, conf):
@@ -207,4 +211,6 @@
         version = self.getCompilerVersion(conf)
         if version < (3, 9, 0) or (Utils.unversioned_sys_platform() == 'darwin' and version < (8, 1, 0)):
             flags['CXXFLAGS'] += ['-Wno-unknown-pragmas']
+        if version < (6, 0, 0):
+            flags['CXXFLAGS'] += ['-Wno-missing-braces'] # Bug #4721
         return flags
diff --git a/.waf-tools/pch.py b/.waf-tools/pch.py
deleted file mode 100644
index 3df299f..0000000
--- a/.waf-tools/pch.py
+++ /dev/null
@@ -1,153 +0,0 @@
-#! /usr/bin/env python
-# encoding: utf-8
-# Alexander Afanasyev (UCLA), 2014
-
-"""
-Enable precompiled C++ header support (currently only clang++ and g++ are supported)
-
-To use this tool, wscript should look like:
-
-	def options(opt):
-		opt.load('pch')
-		# This will add `--with-pch` configure option.
-		# Unless --with-pch during configure stage specified, the precompiled header support is disabled
-
-	def configure(conf):
-		conf.load('pch')
-		# this will set conf.env.WITH_PCH if --with-pch is specified and the supported compiler is used
-		# Unless conf.env.WITH_PCH is set, the precompiled header support is disabled
-
-	def build(bld):
-		bld(features='cxx pch',
-			target='precompiled-headers',
-			name='precompiled-headers',
-			headers='a.h b.h c.h', # headers to pre-compile into `precompiled-headers`
-
-			# Other parameters to compile precompiled headers
-			# includes=...,
-			# export_includes=...,
-			# use=...,
-			# ...
-
-			# Exported parameters will be propagated even if precompiled headers are disabled
-		)
-
-		bld(
-			target='test',
-			features='cxx cxxprogram',
-			source='a.cpp b.cpp d.cpp main.cpp',
-			use='precompiled-headers',
-		)
-
-		# or
-
-		bld(
-			target='test',
-			features='pch cxx cxxprogram',
-			source='a.cpp b.cpp d.cpp main.cpp',
-			headers='a.h b.h c.h',
-		)
-
-Note that precompiled header must have multiple inclusion guards.  If the guards are missing, any benefit of precompiled header will be voided and compilation may fail in some cases.
-"""
-
-import os
-from waflib import Task, TaskGen, Logs, Utils
-from waflib.Tools import c_preproc, cxx
-
-
-PCH_COMPILER_OPTIONS = {
-	'clang++': [['-include'], '.pch', ['-x', 'c++-header']],
-	'g++':     [['-include'], '.gch', ['-x', 'c++-header']],
-}
-
-
-def options(opt):
-	opt.add_option('--without-pch', action='store_false', default=True, dest='with_pch', help='''Try to use precompiled header to speed up compilation (only g++ and clang++)''')
-
-def configure(conf):
-	if (conf.options.with_pch and conf.env['COMPILER_CXX'] in PCH_COMPILER_OPTIONS.keys()):
-		if Utils.unversioned_sys_platform() == "darwin" and conf.env['CXX_NAME'] == 'clang':
-			version = tuple(int(i) for i in conf.env['CC_VERSION'])
-			if version < (6, 1, 0):
-				# Issue #2804
-				return
-		conf.env.WITH_PCH = True
-		flags = PCH_COMPILER_OPTIONS[conf.env['COMPILER_CXX']]
-		conf.env.CXXPCH_F = flags[0]
-		conf.env.CXXPCH_EXT = flags[1]
-		conf.env.CXXPCH_FLAGS = flags[2]
-
-
-@TaskGen.feature('pch')
-@TaskGen.before('process_source')
-def apply_pch(self):
-	if not self.env.WITH_PCH:
-		return
-
-	if getattr(self.bld, 'pch_tasks', None) is None:
-		self.bld.pch_tasks = {}
-
-	if getattr(self, 'headers', None) is None:
-		return
-
-	self.headers = self.to_nodes(self.headers)
-
-	if getattr(self, 'name', None):
-		try:
-			task = self.bld.pch_tasks[self.name]
-			self.bld.fatal("Duplicated 'pch' task with name %r" % self.name)
-		except KeyError:
-			pass
-
-	out = '%s.%d%s' % (self.target, self.idx, self.env['CXXPCH_EXT'])
-	out = self.path.find_or_declare(out)
-	task = self.create_task('gchx', self.headers, out)
-
-	# target should be an absolute path of `out`, but without precompiled header extension
-	task.target = out.abspath()[:-len(out.suffix())]
-
-	self.pch_task = task
-	if getattr(self, 'name', None):
-		self.bld.pch_tasks[self.name] = task
-
-@TaskGen.feature('cxx')
-@TaskGen.after_method('process_source', 'propagate_uselib_vars')
-def add_pch(self):
-	if not (self.env['WITH_PCH'] and getattr(self, 'use', None) and getattr(self, 'compiled_tasks', None) and getattr(self.bld, 'pch_tasks', None)):
-		return
-
-	pch = None
-	# find pch task, if any
-
-	if getattr(self, 'pch_task', None):
-		pch = self.pch_task
-	else:
-		for use in Utils.to_list(self.use):
-			try:
-				pch = self.bld.pch_tasks[use]
-			except KeyError:
-				pass
-
-	if pch:
-		for x in self.compiled_tasks:
-			x.env.append_value('CXXFLAGS', self.env['CXXPCH_F'] + [pch.target])
-
-class gchx(Task.Task):
-	run_str = '${CXX} ${ARCH_ST:ARCH} ${CXXFLAGS} ${CPPFLAGS} ${CXXPCH_FLAGS} ${FRAMEWORKPATH_ST:FRAMEWORKPATH} ${CPPPATH_ST:INCPATHS} ${DEFINES_ST:DEFINES} ${CXXPCH_F:SRC} ${CXX_SRC_F}${SRC[0].abspath()} ${CXX_TGT_F}${TGT[0].abspath()}'
-	scan    = c_preproc.scan
-	color   = 'BLUE'
-	ext_out=['.h']
-
-	def runnable_status(self):
-		try:
-			node_deps = self.generator.bld.node_deps[self.uid()]
-		except KeyError:
-			node_deps = []
-		ret = Task.Task.runnable_status(self)
-		if ret == Task.SKIP_ME and self.env.CXX_NAME == 'clang':
-			t = os.stat(self.outputs[0].abspath()).st_mtime
-			for n in self.inputs + node_deps:
-				if os.stat(n.abspath()).st_mtime > t:
-					return Task.RUN_ME
-		return ret