Remove unnecessary CPPFLAGS and fix the import paths properly. It seems
there was an upstream bug introduced in 2.7.11 (via Red Hat), which broke
the default values. In r295977, we added a hack to override these two
definitions but it was actually incomplete and incorrect, e. g., the import
path for wsdl2h was still not properly set. Now we fix the root cause of
these longstanding problems correctly.