try to wor around faulty autoconf macro.

git-svn-id: svn+ssh://svn.gna.org/svn/gnustep/tools/make/trunk@32684 72102866-910b-0410-8b05-ffd578937521

ChangeLog

@@ -1,3 +1,11 @@
+2011-03-22  Richard Frith-Macdonald <rfm@gnu.org>
+
+	* configure.ac: work around the fact that AC_PROG_CXX is buggy and
+	reports a compiler even when no working compiler exists.  So if a
+	test compilation fails with the compiler it returns, we clear CXX
+	The compilation is done for an Objective-C++ test file since that's
+	what we actually want a C++ compiler for normally.
+
 2011-03-22  Nicola Pero  <nicola.pero@meta-innovation.com>
 
 	* config-noarch.make.in: Updated comment.

configure.ac

@@ -1245,6 +1245,40 @@ ac_cv_objc_threaded="$objc_threaded"
 AC_SUBST(objc_threaded)
 AC_SUBST(ac_cv_objc_threaded)
 
+AC_MSG_CHECKING(whether Objective-C++ is supported)
+AC_LANG_PUSH(C++)
+CXXFLAGS_saved="$CXXFLAGS"
+CXXFLAGS="$CXXFLAGS -x objective-c++"
+CPPFLAGS_saved="$CPPFLAGS"
+CPPFLAGS="$CPPFLAGS -x objective-c++"
+AC_RUN_IFELSE([[
+
+@interface	ObjCClass
+{
+  int x;
+}
+@end
+
+class CppClass
+{
+  int x;
+};
+
+int
+main()
+{
+  return 0;
+}
+]], objcc=yes, objcc=no)
+AC_MSG_RESULT($objcc)
+if test x"$objcc" = x"no"; then
+  CXX=
+fi
+AC_SUBST(CXX)
+CXXFLAGS="$CXXFLAGS_saved"
+CPPFLAGS="$CPPFLAGS_saved"
+AC_LANG_POP(C++)
+
 #--------------------------------------------------------------------
 # Check if GCC supports -fobjc-nonfragile-abi, and if so, turn it on!
 #--------------------------------------------------------------------