cogl: Remove cogl_util_memmem() macro

`cogl_util_memmem` was used as a wrapper in case `memmem` wasn't
defined, but since commit 46942c24 these are required. In case of
`memmem`, we didn't explicitly require this in the meson build files, so
add that as well.

https://gitlab.gnome.org/GNOME/mutter/merge_requests/629

cogl/cogl/cogl-gles2-context.c

@@ -159,7 +159,7 @@ replace_token (char *string,
 
   /* NOTE: this assumes token and replacement are the same length */
 
-  while ((token_pos = _cogl_util_memmem (last_pos,
+  while ((token_pos = memmem (last_pos,
                               end - last_pos,
                               token,
                               token_length)))
@@ -908,7 +908,7 @@ gl_get_shader_source_wrapper (GLuint shader,
 
       /* Strip out the wrapper snippet we added when the source was
        * specified */
-      wrapper_start = _cogl_util_memmem (source,
+      wrapper_start = memmem (source,
                               copy_length,
                               wrapper_marker,
                               sizeof (wrapper_marker) - 1);

cogl/cogl/cogl-util.h

@@ -163,8 +163,6 @@ _cogl_util_pixel_format_from_masks (unsigned long r_mask,
 #define _COGL_STATIC_ASSERT(EXPRESSION, MESSAGE) \
   _Static_assert (EXPRESSION, MESSAGE);
 
-#define _cogl_util_memmem memmem
-
 static inline void
 _cogl_util_scissor_intersect (int rect_x0,
                               int rect_y0,

meson.build

@@ -272,6 +272,7 @@ endif
 required_functions = [
   'ffs',
   'clz',
+  'memmem',
 ]
 foreach function : required_functions
   if not cc.has_function(function)