mingw-w64: All rustbuild tests fail

[petrochenkov]

mingw-w64 toolchain doesn't have cc executable literally (it has gcc for C code), but in all cases except for rustbuild tests the C compiler is correctly found, so supposedly rustbuild tests do something wrong.

The workaround is to copy or symlink gcc as cc somewhere in PATH.

cc @Mark-Simulacrum

running 8 tests
test builder::__test::dist_with_same_targets_and_hosts ... FAILED
test builder::__test::build_with_target_flag ... FAILED
test builder::__test::build_default ... FAILED
test builder::__test::dist_with_target_flag ... FAILED
test builder::__test::dist_with_hosts ... FAILED
test builder::__test::dist_with_targets_and_hosts ... FAILED
test builder::__test::dist_with_targets ... FAILED
test builder::__test::dist_baseline ... FAILED

failures:

---- builder::__test::dist_with_same_targets_and_hosts stdout ----
        thread 'builder::__test::dist_with_same_targets_and_hosts' panicked at '

couldn't find required command: "cc"

', bootstrap\sanity.rs:66:13
note: Run with `RUST_BACKTRACE=1` for a backtrace.

---- builder::__test::build_with_target_flag stdout ----
        thread 'builder::__test::build_with_target_flag' panicked at '

couldn't find required command: "cc"

', bootstrap\sanity.rs:66:13

---- builder::__test::build_default stdout ----
        thread 'builder::__test::build_default' panicked at '

couldn't find required command: "cc"

', bootstrap\sanity.rs:66:13

---- builder::__test::dist_with_target_flag stdout ----
        thread 'builder::__test::dist_with_target_flag' panicked at '

couldn't find required command: "cc"

', bootstrap\sanity.rs:66:13

---- builder::__test::dist_with_hosts stdout ----
        thread 'builder::__test::dist_with_hosts' panicked at '

couldn't find required command: "cc"

', bootstrap\sanity.rs:66:13

---- builder::__test::dist_with_targets_and_hosts stdout ----
        thread 'builder::__test::dist_with_targets_and_hosts' panicked at '

couldn't find required command: "cc"

', bootstrap\sanity.rs:66:13

---- builder::__test::dist_with_targets stdout ----
        thread 'builder::__test::dist_with_targets' panicked at '

couldn't find required command: "cc"

', bootstrap\sanity.rs:66:13

---- builder::__test::dist_baseline stdout ----
        thread 'builder::__test::dist_baseline' panicked at '

couldn't find required command: "cc"

', bootstrap\sanity.rs:66:13

[Mark-Simulacrum]

Do you know if there's an easy way for me to test this without access to a Windows machine?

[petrochenkov]

I.. don't know. I always had access to a Windows machine.

CI maybe? It's an interesting question actually, how this passed our Appveyor testing.

[retep998]

Because our appveyor has all of msys2 in PATH which probably has a cc alias floating around somewhere. We really need to pare down the amount of msys stuff we have in CI's PATH, especially for -msvc where ideally there should be no msys or mingw at all.

[petrochenkov]

Fixed in #50012