CodeGen: Fix invalid bitcast for lifetime.start/end

lifetime.start/end expects pointer argument in alloca address space.
However in C++ a temporary variable is in default address space.

This patch changes API CreateMemTemp and CreateTempAlloca to
get the original alloca instruction and pass it lifetime.start/end.

It only affects targets with non-zero alloca address space.

Differential Revision: https://reviews.llvm.org/D45900

llvm-svn: 332593