Fix win-scons CI (#531)

* scons follow reference to c++ compiler
* don't worry about testing C compiler
* on failure, compile test program
* fix windows DEBUG definition flag
* add source file to win-scons SConscript

This fixes #514

src/tools/SConscript

@@ -31,6 +31,7 @@ if str(platform) == "darwin":
 	tools.extend(Glob("*.mac.*"))
 elif str(platform) == "win32":
 	tools.extend(Glob("*.win.cpp"))
+	tools.extend(Glob("../fileio/*.win.cpp"))
 elif str(platform) == "posix":
 	tools.extend(Glob("*.linux.cpp"))
 	tools.append("prefs.win.cpp")