Breaking changes in Visual C++ 2015

[Walter Bright via Digitalmars-d]

Contrived example:

	// mymod.h
         #ifdef UseFloat
	extern float x;
	#else
         extern int x;
         #endif

	// main.c
         #include <stdio.h>
	#include "mymod.h"
	void main() {
		x = 0;
		printf("%d\n", x);
	}

Compile commands:

	gcc -c mymod.c
	gcc -c -DUseFloat main.c		# <-- oops
	gcc main.o mymod.o



The thing is, every day I compile some modules with -unittest, and some without, 
and link together together. Even if the ones without -unittest are the linked in 
Phobos modules. The autotester does it all day every day, too.

If this didn't work, D's unit tests indeed would be rather useless.