It is now widely recommended that ELF shared libraries hide symbols
except those with explicit __attribute__((visibility("default"))).
This is supported by all major compilers and should rather be an
option in libtool.
* builds/unix/configure.raw: Add -fvisibility=hidden to CFLAGS.
* builds/unix/ftconfig.in, builds/vms/ftconfig.h,
include/freetype/config/ftconfig.h (FT_EXPORT): Use visibility
attribute.