Correctly implement with AC_WITH(glut) so that --without-glut works.

Upstream-Status: Pending
Signed-off-by: Ross Burton <ross.burton@intel.com>

Index: mesa-demos-8.0.1/configure.ac
===================================================================
--- mesa-demos-8.0.1.orig/configure.ac	2010-07-13 19:52:41.000000000 +0100
+++ mesa-demos-8.0.1/configure.ac	2012-11-12 12:49:54.940054571 +0000
@@ -65,21 +65,25 @@
 DEMO_LIBS="$DEMO_LIBS $GL_LIBS"
 
 dnl Check for GLUT
-GLUT_CFLAGS=""
-GLUT_LIBS=-lglut
-glut_enabled=yes
+glut_enabled=no
 AC_ARG_WITH([glut],
 	[AS_HELP_STRING([--with-glut=DIR],
 			[glut install directory])],
 	[GLUT_CFLAGS="-I$withval/include"
-	 GLUT_LIBS="-L$withval/lib -lglut"])
-AC_CHECK_HEADER([GL/glut.h],
-		[],
-		[glut_enabled=no])
-AC_CHECK_LIB([glut],
-		[glutInit],
-		[],
-		[glut_enabled=no])
+	 GLUT_LIBS="-L$withval -lglut"],
+	[GLUT_CFLAGS=""
+	 GLUT_LIBS="-lglut"]
+        )
+AS_IF([test "x$with_glut" != xno],
+      [AC_CHECK_HEADER([GL/glut.h],
+                       [],
+                       [glut_enabled=no])
+       AC_CHECK_LIB([glut],
+                    [glutInit],
+                    [],
+                    [glut_enabled=no])
+       glut_enabled=yes
+])
 
 GLEW_CFLAGS=""
 GLEW_LIBS="-lGLEW"