[build] Use gcc (and clang) in C99 mode.

Other compilers are unchanged.

* builds/compiler/gcc-dev.mk, builds/compiler/gcc.mk (ANSIFLAGS):
s/-ansi/-std=c99/.

* builds/freetype.mk (FT_CFLAGS): Remove `-std=c99`.

* builds/unix/configure.raw: Handle C99.
Remove no longer needed test for gcc 4.6 and earlier.
6 files changed