`is_flag_supported` returns false negative

[tcharding]

When building with the wasm32-unknown-unknown target flags are not getting passed correctly to clang.

cc::Builder::new().flag_if_supported("-Wno-unused-function") ignores the flag but flag("-Wno-unused-function") works.

It looks like is_flag_supported is giving a false negative. I managed to get this error

warning: output: Output { status: ExitStatus(unix_wait_status(256)), stdout: "", stderr: "clang: error: unable to execute command: Executable \"wasm-ld-14\" doesn't exist!\nclang: error: linker command failed with exit code 1 (use -v to see invocation)\n" }

My machine does not have wasm-ld-14 installed, it has wasm-ld-15. I was not able to work out why the wrong version is used in is_flag_supported but the correct version is used when running try_compile.

[dot-asm]

Community solution was suggested in #839.

[thomcc]

That one had slipped under my radar (Had been pretty busy with $DAYJOB around the time it was submitted). I've merged it, and it should be in the next release.

[tcharding]

Awesome, thanks!