[PATCH] Enable UBSan on Windows

[Ed Maste]

================
Comment at: lib/ubsan/ubsan_value.h:17
@@ -16,3 +16,3 @@
 
 // For now, only support Linux, FreeBSD and Darwin. Other platforms should
 // be easy to add, and probably work as-is.
----------------
akhaldi wrote:
> timurrrr wrote:
> > You should probably update the comment.
> Noted.
It's clear from the following #if conditions which platforms are supported, no point in repeating the list in a comment immediately prior.  How about:
```
// Only certain platforms are supported. Others should be easy to add, and may work as-is.
```

http://reviews.llvm.org/D5368