opal_setup_cc.m4: don't use -finline-functions with clang

Some versions of clang (at least >= 3.5 -- perhaps older versions,
too?) will *warn* about -finline-functions, but still allow it.  This
is very annoying, so check for that warning, too.

config/opal_setup_cc.m4

@@ -196,12 +196,26 @@ AC_DEFUN([OPAL_SETUP_CC],[
     if test "$GCC" = "yes"; then
         CFLAGS_orig="$CFLAGS"
 
+        # Note: Some versions of clang (at least >= 3.5 -- perhaps
+        # older versions, too?) will *warn* about -finline-functions,
+        # but still allow it.  This is very annoying, so check for
+        # that warning, too.
         CFLAGS="$CFLAGS_orig -finline-functions"
         add=
         AC_CACHE_CHECK([if $CC supports -finline-functions],
                    [opal_cv_cc_finline_functions],
                    [AC_TRY_COMPILE([], [],
-                                   [opal_cv_cc_finline_functions="yes"],
+                                   [opal_cv_cc_finline_functions="yes"
+                                    if test -s conftest.err ; then
+                                        for i in unused 'not supported' ; do
+                                            $GREP -iq "$i" conftest.err
+                                            if test $? -eq 0; then
+                                                opal_cv_cc_finline_functions="no"
+                                                break;
+                                            fi
+                                        done
+                                    fi
+                                   ],
                                    [opal_cv_cc_finline_functions="no"])])
         if test "$opal_cv_cc_finline_functions" = "yes" ; then
             add=" -finline-functions"