tests/cogl: Migrate no-gl header test

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2555>

cogl/tests/conform/meson.build

@@ -1,6 +1,5 @@
 cogl_test_conformance_sources = [
   'test-conform-main.c',
-  'test-no-gl-header.c',
   'test-version.c',
   'test-layer-remove.c',
   'test-alpha-test.c',

src/tests/cogl/conform/meson.build

@@ -24,6 +24,7 @@ cogl_tests = [
   [ 'test-point-size-attribute', [] ],
   [ 'test-point-sprite', [] ],
   [ 'test-point-sprite-known-failure', ['gl', 'gl3', 'gles2'] ],
+  [ 'test-no-gl-header', [] ],
 ]
 
 cogl_test_conformance_includes = [

src/tests/cogl/conform/test-no-gl-header.c

@@ -7,10 +7,9 @@
 #error "Including cogl.h shouldn't be including any GL headers"
 #endif
 
-void test_no_gl_header (void);
-
-void
-test_no_gl_header (void)
+int
+main (int    argc,
+      char **argv)
 {
+  return EXIT_SUCCESS;
 }
-