complibs/ppl: only add -fpermissive flag to CXXFLAGS
-fpermissive is not a valid option to gcc.
Adding it to the CFLAGS make the ppl checks fail with the following
error:
[ALL ] Making check in tests
[ALL ] cc1: warnings being treated as errors
[ERROR] cc1: error: command line option "-fpermissive" is valid for C++/ObjC++ but not for C
[ALL ] cc1: warnings being treated as errors
[ERROR] cc1: error: command line option "-fpermissive" is valid for C++/ObjC++ but not for C
[ERROR] make[7]: *** [formatted_output.o] Error 1