configure: Deal with missing macro a bit better.

The AX_CXX_COMPILE_STDCXX_11 macro is found in the autoconf-archive
package. If this is not installed, invoking the macro spits out an
error message that makes it look like a syntax error. This wraps it
in a check.

diff --git a/configure.ac b/configure.ac
index eac88f1f61b216767663a02cecde711fb1124598..db6f644e4ddce3cd72d8ec8bcf9c476d6b18c491 100644 (file)
--- a/configure.ac
+++ b/configure.ac
@@ -173,7 +173,8 @@ AC_ARG_ENABLE(java,
 
 # Check if the C++ compiler supports the C++11 standard.
 
-AX_CXX_COMPILE_STDCXX_11(,[optional])
+m4_ifdef([AX_CXX_COMPILE_STDCXX_11], [AX_CXX_COMPILE_STDCXX_11(,[optional])],
+       [AC_MSG_NOTICE([Missing macro m4_toupper(aX_CXX_COMPILE_STDCXX_11), no C++11 check])])
 
 if test "x$HAVE_CXX11" != "x1"; then
        BINDINGS_CXX="no"