build: Correcting library detection

When detecting location of the library, `includes` and `libpath`
variables must be used instead of `cxxflags` and `linkflags`.  While the
latter also makes everything work, it results in unexpected behavior:
waf always adds LINKFLAGS* in the beginning of the linking command,
which can screw up order in which libraries are selected (e.g.,
system-installed library can be chosen instead of the compiled version).

Change-Id: I9ed36e8a4e8523b33ca2e88414aed8de5111c9cd
diff --git a/.waf-tools/cryptopp.py b/.waf-tools/cryptopp.py
index 2f95504..320c81f 100644
--- a/.waf-tools/cryptopp.py
+++ b/.waf-tools/cryptopp.py
@@ -84,8 +84,8 @@
     val = self.check_cxx(msg='Checking if CryptoPP library works',
                          header_name='cryptopp/config.h',
                          lib='cryptopp',
-                         cxxflags="-I%s/include" % root,
-                         linkflags="-L%s/lib" % root,
+                         includes="%s/include" % root,
+                         libpath="%s/lib" % root,
                          mandatory=mandatory,
                          use=use,
                          uselib_store=var)