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

Signed-off-by: "Samuel Martin" <smartin@aldebaran-robotics.com>
Message-Id: <bba2482a06a11415207e.1365876457@smartin-de-2.aldebaran.lan>
Patchwork-Id: 236383

# Menu for the native GDB

config GDB_NATIVE

    bool

    prompt "Native gdb"

    depends on ! BARE_METAL

    depends on ! BACKEND

    help

      Build and install a native gdb for the target, to run on the target.

if GDB_NATIVE

config GDB_NATIVE_STATIC

    bool

    prompt "Build a static native gdb"

    help

      In case you have trouble with dynamic loading of shared libraries,

      you will find that a static gdb comes in handy.

endif # GDB_NATIVE