[mips] Fix more incorrect uses of HasMips64 and isMips64()

Summary:
- Conditional moves acting on 64-bit GPR's should require MIPS-IV rather than MIPS64
- ISD::MUL, and ISD::MULH[US] should be lowered on all 64-bit ISA's

Patch by David Chisnall
His work was sponsored by: DARPA, AFRL

I've added additional testcases to cover as much of the codegen changes
affecting MIPS-IV as I can. Where I've been unable to find an existing
MIPS64 testcase that can be re-used for MIPS-IV (mainly tests covering
ISD::GlobalAddress and similar), I at least agree that MIPS-IV should
behave like MIPS64. Further testcases that are fixed by this patch will follow
in my next commit. The testcases from that commit that fail for MIPS-IV without
this patch are:
    LLVM :: CodeGen/Mips/2010-07-20-Switch.ll
    LLVM :: CodeGen/Mips/cmov.ll
    LLVM :: CodeGen/Mips/eh-dwarf-cfa.ll
    LLVM :: CodeGen/Mips/largeimmprinting.ll
    LLVM :: CodeGen/Mips/longbranch.ll
    LLVM :: CodeGen/Mips/mips64-f128.ll
    LLVM :: CodeGen/Mips/mips64directive.ll
    LLVM :: CodeGen/Mips/mips64ext.ll
    LLVM :: CodeGen/Mips/mips64fpldst.ll
    LLVM :: CodeGen/Mips/mips64intldst.ll
    LLVM :: CodeGen/Mips/mips64load-store-left-right.ll
    LLVM :: CodeGen/Mips/sint-fp-store_pattern.ll

Reviewers: dsanders

Reviewed By: dsanders

CC: matheusalmeida

Differential Revision: http://reviews.llvm.org/D3343
Define a new macro in libc++ named '_LIBCPP_HAS_NO_ASAN'. When this is defined,
libc++ will not call address_sanitizer to detect addressing errors in the
standard library containers. This is a negative macro to enable users to
disable the libc++ checks even if they are compiling with address sanitizer
enabled by defining this macro.

At the present time, there is no code in libc++ that looks at this macro.
That will come soon. This is just infrastructure.