configure --enable-stack-protector works with C++ sources as well

configure.ac

@@ -89,7 +89,7 @@ PKG_CHECK_MODULES([RE2], [re2])
 # df7a2dc in re2, the pointer may be NULL, if we just want to know
 # whether there was a match. This check tests for that feature.
 # Note: the test may cause a core dump if it fails.
-AC_LANG(C++)
+AC_LANG_PUSH(C++)
 SAVE_CXXFLAGS="$CXXFLAGS"
 SAVE_LDFLAGS="$LDFLAGS"
 CXXFLAGS+=" -std=c++11"
@@ -109,7 +109,7 @@ main() {
 	)
 CXXFLAGS="$SAVE_CXXFLAGS"
 LDFLAGS="$SAVE_LDFLAGS"
-AC_LANG(C)
+AC_LANG_POP()
 
 # --enable-stack-protector
 AC_ARG_ENABLE(stack-protector,
@@ -122,6 +122,12 @@ if test "x$enable_stack_protector" != "xno"; then
 		AX_CHECK_LINK_FLAG([-fstack-protector],
 			[CFLAGS="${CFLAGS} -fstack-protector"], [], []),
 		[], [])
+	AC_LANG_PUSH(C++)
+	AX_CHECK_COMPILE_FLAG([-fstack-protector],
+		AX_CHECK_LINK_FLAG([-fstack-protector],
+			[CXXFLAGS="${CXXFLAGS} -fstack-protector"], [], []),
+		[], [])
+	AC_LANG_POP()
 fi
 
 # --enable-debugging