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

[Kostya Serebryany]

I will let Dmitry review this in detail, but my general request is to avoid #ifdefs inside the code as much as possible. 
Please try to move asm many #ifdefs as you can into headers and then use plain if() in the code. 
For example, you can do if(SANITIZER_CAN_USE_ALLOCATOR64) instead of #ifdef SANITIZER_CAN_USE_ALLOCATOR64

http://reviews.llvm.org/D6291