GNU/Hurd fixes

Here is a couple of fixes for GNU/Hurd:
- dri_interface.h: no libdrm support either.
- configure.ac:
 - GNU/Hurd is a GNU OS with _GNU_SOURCE and PTHREADS.
 - GNU needs a couple of flags like other OSes

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

configure.ac

@@ -87,7 +87,7 @@ dnl Compiler macros
 DEFINES=""
 AC_SUBST([DEFINES])
 case "$host_os" in
-linux*|*-gnu*)
+linux*|*-gnu*|gnu*)
     DEFINES="$DEFINES -D_GNU_SOURCE -DPTHREADS"
     ;;
 solaris*)
@@ -742,6 +742,10 @@ if test "$mesa_driver" = dri; then
                 unichrome savage sis swrast"
         fi
         ;;
+    gnu*)
+        DEFINES="$DEFINES -DUSE_EXTERNAL_DXTN_LIB=1 -DIN_DRI_DRIVER"
+        DEFINES="$DEFINES -DGLX_INDIRECT_RENDERING -DHAVE_ALIAS"
+	;;
     solaris*)
         DEFINES="$DEFINES -DUSE_EXTERNAL_DXTN_LIB=1 -DIN_DRI_DRIVER"
         DEFINES="$DEFINES -DGLX_INDIRECT_RENDERING"

include/GL/internal/dri_interface.h

@@ -41,7 +41,7 @@
 #define DRI_INTERFACE_H
 
 /* For archs with no drm.h */
-#if !defined(__APPLE__) && !defined(__CYGWIN__)
+#if !defined(__APPLE__) && !defined(__CYGWIN__) && !defined(__GNU__)
 #include <drm.h>
 #else
 typedef unsigned int drm_context_t;