This emits CodeView debug info for heapallocsite by emitting labels around
the call instructions. The metadata is passed through instruction selection by mapping SDNodes to metadata.
https://reviews.llvm.org/D60800 is a previous change to emit the metadata
when FastISel is used.
Related to bug https://bugs.llvm.org/show_bug.cgi?id=38491
This is a recommit of https://reviews.llvm.org/D61105