configure.ac: fix cross-compilation

AC_CHECK_FILE can't be used when cross-compiling

[Retrieved from:
https://git.buildroot.net/buildroot/tree/package/x11r7/xdriver_xf86-video-sis/0001-cross.patch]
Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>

configure.ac

@@ -75,12 +75,18 @@ sdkdir=`$PKG_CONFIG --variable=sdkdir xorg-server`
 # Checks for libraries.
 
 if test "$DRI" != no; then
-        AC_CHECK_FILE([${sdkdir}/dri.h],
-                      [have_dri_h="yes"], [have_dri_h="no"])
-        AC_CHECK_FILE([${sdkdir}/sarea.h],
-                      [have_sarea_h="yes"], [have_sarea_h="no"])
-        AC_CHECK_FILE([${sdkdir}/dristruct.h],
-                      [have_dristruct_h="yes"], [have_dristruct_h="no"])
+        if test "$cross_compiling" = "no" ; then
+               AC_CHECK_FILE([${sdkdir}/dri.h],
+                             [have_dri_h="yes"], [have_dri_h="no"])
+               AC_CHECK_FILE([${sdkdir}/sarea.h],
+                             [have_sarea_h="yes"], [have_sarea_h="no"])
+               AC_CHECK_FILE([${sdkdir}/dristruct.h],
+                             [have_dristruct_h="yes"], [have_dristruct_h="no"])
+        else
+		have_dri_h="yes"
+		have_sarea_h="yes"
+		have_dristruct_h="yes"
+        fi
 fi
 
 AC_MSG_CHECKING([whether to include DRI support])