Add C++11 compiler support detection feature

This is currently copied from http://quickgit.kde.org/index.php?p=scratch%2Fdakon%2Fcmake-cxx11.git
but there is a chance that in future it will be merged into CMake proper.

cmake/Modules/CheckCXX11Features/cxx11-test-sizeof_member.cpp

@@ -0,0 +1,14 @@
+struct foo {
+	char bar;
+	int baz;
+};
+
+int main(void)
+{
+	bool ret = (
+		(sizeof(foo::bar) == 1) &&
+		(sizeof(foo::baz) >= sizeof(foo::bar)) &&
+		(sizeof(foo) >= sizeof(foo::bar) + sizeof(foo::baz))
+	);
+	return ret ? 0 : 1;
+}