[msan] Avoid redundant origin stores.

Origin is meaningless for fully initialized values. Avoid
storing origin for function arguments that are known to
be always initialized (i.e. shadow is a compile-time null
constant).

This is not about correctness, but purely an optimization.
Seems to affect compilation time of blacklisted functions
significantly.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@213239 91177308-0d34-0410-b5e6-96231b3b80d8
Fix the prefix for arm64 triple

Triple.cpp still returns "arm64" as prefix for arm64 triple, causing Clang not
being able to select the correct GCCBuiltin IR.

This patch changes the value to correct prefix "aarch64". Regression test will
be added in the coming patch.

Differential Revision: http://reviews.llvm.org/D4516


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@213240 91177308-0d34-0410-b5e6-96231b3b80d8