[build] Split off more stuff from `ftconfig.h'.

* builds/unix/ftconfig.h.in, builds/vms/ftconfig.h,
include/freetype/config/ftconfig.h: Split off macro definitions
required by the FreeType API headers to...
* include/freetype/config/public-macros.h: ...this new file.

* builds/unix/ftconfig.h.in, builds/vms/ftconfig.h,
include/freetype/config/ftconfig.h: Split off macro definitions used
by the library but not to be exposed to clients to...
* include/freetype/config/compiler-macros.h: ...this new file.

* include/freetype/internal/*.h, src/raster/ftraster.h: Include
`compiler-macros.h' where needed.
14 files changed