Since r199356, we've printed a warning when dropping debug info.
r225562 started crashing on that, since it registered a diagnostic
handler that only expected errors. This fixes the handler to expect
other severities. As a side effect, it now prints "error: " at the
start of error messages, similar to `llvm-as`.
There was a testcase for r199356, but it only really checked the
assembler. Move `test/Bitcode/drop-debug-info.ll` to `test/Assembler`,
and introduce `test/Bitcode/drop-debug-info.3.5.ll` (and companion
`.bc`) to test the bitcode reader.
Note: tools/gold/gold-plugin.cpp has an equivalent bug, but I'm not sure
what the best fix is there. I'll file a PR.
llvm-svn: 230416
serge-sans-paille