Rewrite the checks from r233164 that I temporarily disabled in r233165.
It turns out that the line-tables only debug info we emit from `llc` is
(intentionally) different on Linux than on Darwin. r218129 started
skipping emission of subprograms with no inlined subroutines, and
r218702 was a spiritual revert of that behaviour for Darwin.
I think we can still test this in a platform-neutral way.
- Stop checking for the possibly missing `DW_TAG_subprogram` defining
the debug info for the real version of `@foo`.
- Start checking the line tables, ensuring that the right debug info
was used to generate them (grabbing `DW_AT_low_pc` from the compile
unit).
- I changed up the line numbers used in the "weak" version so it's
easier to follow.
This should hopefully finish off PR22792.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@233207 91177308-0d34-0410-b5e6-96231b3b80d8
151bc36220