Include p_compiler.h from u_debug.h to fix -Wpedantic warnings:

In file included from ../src/mesa/util/u_memory.h:37,
                 from ../src/mesa/util/hash_table.c:50:
../src/mesa/util/fast_urem_by_const.h: In function ‘util_fast_urem32’:
../src/mesa/util/u_debug.h:187:94: warning: ISO C does not support ‘__FUNCTION__’ predefined identifier [-Wpedantic]
  187 | #define debug_assert(expr) ((expr) ? (void)0 : _debug_assert_fail(#expr, __FILE__, __LINE__, __FUNCTION__))
      |                                                                                              ^~~~~~~~~~~~
../src/mesa/util/u_debug.h:197:22: note: in expansion of macro ‘debug_assert’
  197 | #define assert(expr) debug_assert(expr)
      |                      ^~~~~~~~~~~~
../src/mesa/util/fast_urem_by_const.h:71:4: note: in expansion of macro ‘assert’
   71 |    assert(result == n % d);
      |    ^~~~~~

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Part-of: <!1030>