ARM: Use a dedicated intrinsic for vector bitwise select.

ARM: Use a dedicated intrinsic for vector bitwise select.

The expression based expansion too often results in IR level optimizations
splitting the intermediate values into separate basic blocks, preventing
the formation of the VBSL instruction as the code author intended. In
particular, LICM would often hoist part of the computation out of a loop.

rdar://11011471

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@164342 91177308-0d34-0410-b5e6-96231b3b80d8