mesa: Change _mesa_exec_malloc argument type.

mesa: Change _mesa_exec_malloc argument type.

Fix build error.

In file included from ../src/mesa/x86/rtasm/x86sse.c:7:0:
../src/mesa/main/execmem.h:31:19: error: unknown type name ‘GLuint’; did you mean ‘uint’?
 _mesa_exec_malloc(GLuint size);
                   ^~~~~~
                   uint

Suggested-by: Marek Olšák <marek.olsak@amd.com>
Fixes: e5339fe4a47c ("Move compiler.h and imports.h/c from src/mesa/main into src/util")
Signed-off-by: Vinson Lee <vlee@freedesktop.org>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4361>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4361>