build: Updated precompiled header support (enabled by default)

Change-Id: Iaab62c740ac87b84256a3f71d934760865a54be5
diff --git a/.waf-tools/sphinx_build.py b/.waf-tools/sphinx_build.py
index bd3905b..e61da6e 100644
--- a/.waf-tools/sphinx_build.py
+++ b/.waf-tools/sphinx_build.py
@@ -12,8 +12,8 @@
 
     def __str__(self):
         env = self.env
-        src_str = ' '.join([a.nice_path()for a in self.inputs])
-        tgt_str = ' '.join([a.nice_path()for a in self.outputs])
+        src_str = ' '.join([a.path_from(a.ctx.launch_node()) for a in self.inputs])
+        tgt_str = ' '.join([a.path_from(a.ctx.launch_node()) for a in self.outputs])
         if self.outputs: sep = ' -> '
         else: sep = ''
         return'%s [%s]: %s%s%s\n'%(self.__class__.__name__.replace('_task',''),