[PATCH] [MSan] [MIPS] Adding support for MIPS64

[Mohit Bhakkad]

@kcc @samsonov :Thanks for your comments.

To make MSan work on MIPS, there are 2 more patches:



  - LLVM code: kShadowMask and kOriginOffset are to be defined for MIPS:
 
```
  lib/Transforms/Instrumentation/MemorySanitizer.cpp#L123

```


  - Clang code: to enable memory option for mips. 
   
```
lib/Driver/SanitizerArgs.cpp#L272

```
I just wanted to ask if I should submit those patches for review, or wait till this one is merged.

http://reviews.llvm.org/D5906