Use GLUT_CFLAGS when building glut

Fix this build error (in MesaGLUT-7.6.1)...
glut_cmap.c:23:66: error: X11/Xmu/StdCmap.h: No such file or directory

...by not preventing the cflags that pkg-config finds for glut dependencies
(including 'xmu') from being used.

Defining GLUT_CFLAGS before running the pkg-config prevents the
cflags found by pkg-config from being used.

This patch lets GLUT_CFLAGS that configure & pkg-config work
so hard to set actually get used.

Also make sure the generated configs/autoconf defines GLUT_CFLAGS
used in (at least) src/glut/glx/Makefile.

Signed-off-by: Dan Nicholson <dbn.lists@gmail.com>

configs/autoconf.in

@@ -31,6 +31,7 @@ X11_CFLAGS = @X11_CFLAGS@
 LLVM_CFLAGS = @LLVM_CFLAGS@
 LLVM_LDFLAGS = @LLVM_LDFLAGS@
 LLVM_LIBS = @LLVM_LIBS@
+GLUT_CFLAGS = @GLUT_CFLAGS@
 
 
 # Source selection

configure.ac

@@ -1118,10 +1118,6 @@ fi
 
 if test "x$enable_glut" = xyes; then
     SRC_DIRS="$SRC_DIRS glut/glx"
-    GLUT_CFLAGS=""
-    if test "x$GCC" = xyes; then
-        GLUT_CFLAGS="-fexceptions"
-    fi
     if test "$x11_pkgconfig" = yes; then
         PKG_CHECK_MODULES([GLUT],[x11 xmu xi])
         GLUT_PC_REQ_PRIV="x11 xmu xi"
@@ -1132,6 +1128,9 @@ if test "x$enable_glut" = xyes; then
         GLUT_PC_LIB_PRIV="$GLUT_LIB_DEPS"
         GLUT_PC_CFLAGS="$X11_INCLUDES"
     fi
+    if test "x$GCC" = xyes; then
+        GLUT_CFLAGS="$GLUT_CFLAGS -fexceptions"
+    fi
     GLUT_LIB_DEPS="$GLUT_LIB_DEPS -lm"
     GLUT_PC_LIB_PRIV="$GLUT_PC_LIB_PRIV -lm"