[DebugInfo][InstrRef][X86] Instrument expanded DYN_ALLOCAs

If we have a DYN_ALLOCA_* instruction, it will eventually be expanded to a
stack probe and subtract-from-SP. Add debug-info instrumentation to
X86FrameLowering::emitStackProbe so that it can redirect debug-info for the
DYN_ALLOCA to the lowered stack probe. In practice, this means putting an
instruction number label either the call instruction to _chkstk for win32,
or more commonly on the subtract from SP instruction. The two tests added
cover both of these cases.

Differential Revision: https://reviews.llvm.org/D114452