`-O -C lto` is *not* same to `-C opt-level=2 -C lto`

[lifthrasiir]

Fallout of #21191. -C opt-level=2 sets CodegenOptions::opt_level but -O doesn't, and -C lto path only looks at that. Due to the fallback from LTO path, -O -C lto is currently same to -C opt-level=0 -C lto (!).

[dotdash]

Thanks for the bug report, this will be fixed by #22530

[lifthrasiir]

Ah indeed. This was a duplicate of #22525. Closing.