tgsi: Fix conflict with fortify printf redirect in glibc.

 Fixes clang error:

   tgsi/tgsi_dump.c:72:12: error: no member named '__printf_chk' in 'struct dump_ctx'
         ctx->printf( ctx, "%u", e );
         ~~~  ^
   /usr/include/bits/stdio2.h:109:3: note: expanded from macro 'printf'
     __printf_chk (__USE_FORTIFY_LEVEL - 1, __VA_ARGS__)
     ^

 Idea stolen from:
   http://www.mail-archive.com/pld-cvs-commit@lists.pld-linux.org/msg210998.html

Reviewed-by: Brian Paul <brianp@vmware.com>