Add test for including unguarded windows.h

If you do this, you are wrong, but apparently people expect libraries
to work around intrusive lower cased macros. Oh well.

projects/ExtraTests/X90-WindowsHeaderInclusion.cpp

@@ -0,0 +1,12 @@
+// X90-WindowsHeaderInclusion.cpp
+// Test that the Catch2 header compiles even after including windows.h
+// without defining NOMINMAX first. As an FYI, if you do that, you are
+// wrong.
+
+#include <windows.h>
+#define CATCH_CONFIG_MAIN
+#include <catch2/catch.hpp>
+
+TEST_CASE("Catch2 did survive compilation with windows.h", "[compile-test]") {
+    SUCCEED();
+}