GitLab

gcc objects to using -fvisibility-inlines-hidden with C code:

  cc1: error: command line option "-fvisibility-inlines-hidden"
  is valid for C++/ObjC++ but not for C

Move it from CFLAGS to CPPFLAGS.

Change-Id: I151530748b0d083d8edb50df94db23d101ad01c6