LDC 1.5: Failing LLVM assertion with `-g -enable-inlining`

[kinke]

See #2252 (comment) and https://bugs.llvm.org/show_bug.cgi?id=34834; current CI workaround: ldc-developers/dmd-testsuite@f447afd.

[kinke]

Oh this seems very much like a duplicate of #1989, so the problem most likely isn't specific to LLVM 5.0 LDC 1.5.