[test] Avoid writing to a potentially write-protected dir (#89242)

These tests just don't check the output written to the current directory. The
current directory may be write protected e.g. in a sandboxed environment.

The Testcases that use -emit-llvm and -verify only care about stdout/stderr
and are in this patch changed to use -emit-llvm-only to avoid writing to an
output file. The verify-inlineasmbr.mir testcase that also only care about
stdout/stderr is in this patch changed to throw away the output file and just
write to /dev/null.