glapi: don't walk backwards for includes

Instead just set the proper -I flags and include it from a more standard
path. In this case we'll add -Isrc/mesa (which is common), and #include
main/foo.h.

Signed-off-by: Dylan Baker <dylanx.c.baker@intel.com>
Reviewed-by: Eric Engestrom <eric.engestrom@imgtec.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>

src/mapi/glapi/tests/check_table.cpp

@@ -22,7 +22,7 @@
  */
 
 #include <gtest/gtest.h>
-#include "../mesa/main/glheader.h"
+#include "main/glheader.h"
 
 extern "C" {
 #include "glapi/glapi.h"