Assembler failures are silently ignored #11593
Description
Split from #11377, where we encountered an issue during the assembler that was missed because assembler errors are silently ignored. This made it harder to diagnose the issue as we had to hack the toolchain to get it to spit out the error message from the assembler. The issue manifested as an empty object file, causing a linker failure down the road.
This issue tracks displaying the error message when the assembler fails in the Swift toolchain, as the core issue from #11377 has been fixed.