make: Don't traverse backwards through include directories.

Traversing back through includes is bad idea and should be avoided.
In the case here - indirect_size.h is located in the build directory
$(top_builddir)/src/glx/.

v3: - Update commit message with message provided by Emil

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

src/glx/tests/Makefile.am

@@ -5,6 +5,7 @@ AM_CPPFLAGS = \
 	-I$(top_srcdir)/src \
 	-I$(top_srcdir)/src/mapi \
 	-I$(top_srcdir)/src/mesa \
+	-I$(top_builddir)/src/glx \
 	-I$(top_srcdir)/src/glx \
 	-I$(top_srcdir)/include \
 	-I$(top_srcdir)/include/GL/internal \

src/glx/tests/enum_sizes.cpp

@@ -36,7 +36,7 @@
 #include <gtest/gtest.h>
 #include <GL/gl.h>
 extern "C" {
-#include "../indirect_size.h"
+#include "indirect_size.h"
 }
 
 TEST(ValidEnumSizes, CallLists)