build: Extending wscript to enable coverage information with --with-coverage option

When coverage option is enabled, all necessary flags are exported via
pkgconfig configuration.

Change-Id: Ieac8c17b2b81568fddbfd61d99bb79a5e2b99f13
refs: #1215
diff --git a/libndn-cpp-dev.pc.in b/libndn-cpp-dev.pc.in
index 4b0e793..be52ba0 100644
--- a/libndn-cpp-dev.pc.in
+++ b/libndn-cpp-dev.pc.in
@@ -6,5 +6,5 @@
 Name: libndn-cpp-dev
 Description: Development version of C++ API for NDN (NDN-TLV packet format)
 Version: @VERSION@
-Libs: -L${libdir} @EXTRA_LDFLAGS@ -lndn-cpp-dev @EXTRA_LIBS@ @EXTRA_FRAMEWORKS@
-Cflags: -I${includedir} @EXTRA_INCLUDES@
+Libs: -L${libdir} @EXTRA_LINKFLAGS@ @EXTRA_LDFLAGS@ -lndn-cpp-dev @EXTRA_LIBS@ @EXTRA_FRAMEWORKS@
+Cflags: -I${includedir} @EXTRA_CXXFLAGS@ @EXTRA_INCLUDES@