Fix a bug in gcov instrumentation introduced by r195513. <rdar://15930350>

The entry block of a function starts with all the static allocas. The change
in r195513 splits the block before those allocas, which has the effect of
turning them into dynamic allocas. That breaks all sorts of things. Change to
split after the initial allocas, and also add a comment explaining why the
block is split.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@200515 91177308-0d34-0410-b5e6-96231b3b80d8
Move address override handling in X86MCCodeEmitter to a place where it works for VEX encoded instructions too. This allows 32-bit addressing to work in 64-bit mode.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@200516 91177308-0d34-0410-b5e6-96231b3b80d8
Move address override handling in X86CodeEmitter to a place where it works for VEX encoded instructions too. This allows 32-bit addressing to work in 64-bit mode.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@200517 91177308-0d34-0410-b5e6-96231b3b80d8