sparse: Add GCC pre-defined macros for user-space

sparse: Add GCC pre-defined macros for user-space

Sparse produces a bunch of warnings like this when compiling against
glibc:

  /usr/lib/gcc/i486-linux-gnu/4.3.2//include-fixed/limits.h:33:22: warning: undefined preprocessor identifier '__INT_MAX__'
  /usr/lib/gcc/i486-linux-gnu/4.3.2//include-fixed/limits.h:64:5: warning: undefined preprocessor identifier '__SHRT_MAX__'
  /usr/lib/gcc/i486-linux-gnu/4.3.2//include-fixed/limits.h:64:21: warning: undefined preprocessor identifier '__INT_MAX__'
  /usr/include/bits/xopen_lim.h:95:6: warning: undefined preprocessor identifier '__INT_MAX__'
  /usr/include/bits/xopen_lim.h:98:7: warning: undefined preprocessor identifier '__INT_MAX__'

Fix that up by adding some add_pre_buffer() calls to
create_builtin_define(). For future reference, GCC defines the builtins
in the c_cpp_builtins() function in gcc/c-cppbuiltin.c.

Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>
Acked-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Christopher Li <sparse@chrisli.org>