+# Detect warning flags supported by the compiler, append them to WARN_CFLAGS.
+#
+# Pass -Werror as an extra flag during the test: this is needed to make the
+# -Wunknown-warning-option diagnostic fatal with clang.
+AX_APPEND_COMPILE_FLAGS([ dnl
+ -Wall dnl
+ ],
+ [WARN_CFLAGS],
+ [-Werror])
+
+# When given, add -Werror to WARN_CFLAGS.
+AC_ARG_ENABLE([Werror],
+ [AS_HELP_STRING([--enable-Werror], [Treat compiler warnings as errors.])]
+)
+AS_IF([test "x$enable_Werror" = "xyes"],
+ [WARN_CFLAGS="${WARN_CFLAGS} -Werror"]
+)
+