clover: use the unified check for c++11 instead of the gcc version number

So far clover based its test for compiler support on the version of gcc,
while in reality support for c++11 is required. This patch replaces the
version check by the check unified for all modules that require c++11.

Reviewed-by: Emil Velikov <emil.velikov@collabora.com>

configure.ac

@@ -2294,8 +2294,8 @@ if test "x$enable_opencl" = xyes; then
         AC_MSG_ERROR([cannot enable OpenCL without Gallium])
     fi
 
-    if test $GCC_VERSION_MAJOR -lt 4 -o $GCC_VERSION_MAJOR -eq 4 -a $GCC_VERSION_MINOR -lt 7; then
-        AC_MSG_ERROR([gcc >= 4.7 is required to build clover])
+    if test "x$HAVE_CXX11" != "xyes"; then
+       AC_MSG_ERROR([clover requires c++11 support])
     fi
 
     if test "x$have_libclc" = xno; then