-o no longer works as expected for multiple output types

[nagisa]

$ rustc test.rs --emit=asm,llvm-ir -O --crate-type=rlib -o testold

emits single file testold with LLVM-IR in it. Previously it used to emit testold.s and testold.ll.

This is a stable→stable regression. 1.14.0 works as expected, 1.16.0 does not. Did not test 1.15.0.

[arielb1]

"Intentional" change - #38840. Not marked relnotes. cc @nrc

[alexcrichton]

@arielb1 did you perhaps mean to link a different PR?

[brson]

#38840

[brson]

I took the liberty of P-high, but somebody needs to be assigned cc @rust-lang/compiler @rust-lang/tools