+## Hack to detect a buggy GCC version.
+if test "x$GCC" = xyes \
+ && test x"`$CC --version 2> /dev/null | grep 'gcc.* 4.5.0'`" != x \
+ && test x"`echo $CFLAGS | grep '\-O@<:@23@:>@'`" != x \
+ && test x"`echo $CFLAGS | grep '\-fno-optimize-sibling-calls'`" = x; then
+ AC_MSG_ERROR([GCC 4.5.0 has problems compiling Emacs; see etc/PROBLEMS'.])
+fi
+