glsl: make builtin_mem_ctx a static

This isn't used outside the generated file.

Reviewed-by: Matt Turner <mattst88@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

src/glsl/builtins/tools/generate_builtins.py

@@ -225,7 +225,7 @@ read_builtins(GLenum target, const char *protos, const char **functions, unsigne
     print 'static gl_shader *builtin_profiles[%d];' % len(profiles)
 
     print """
-void *builtin_mem_ctx = NULL;
+static void *builtin_mem_ctx = NULL;
 
 void
 _mesa_glsl_release_functions(void)