debuginfo: Add support for simd types
debuginfo: Move test case from run-pass to debug-info directory so it does not interfere with RUSTFLAGS=-g
debuginfo: Fix a RUSTFLAGS incompatibility in test runner.
debuginfo: Re-enable test case that should have worked all along.
auto merge of #12399 : michaelwoerister/rust/simd-fix, r=alexcrichton

Fixes  #12333.
I also re-enabled the *function-arg-initialization* test case, so if it passes again, fixes #12021.