Auto merge of #2621 - RalfJung:windows-gnu, r=RalfJung
Auto merge of #2621 - RalfJung:windows-gnu, r=RalfJung

test on windows-gnu target

The windows-gnu target for an open-source windows toolchain is slightly different in some low-level aspects of the standard library, such as TLS handling. So let's separately ensure that this works. (Also tests a 64bit windows target on a windows host, which we didn't have so far.)

rust-lang/miri,rust-lang/miri,rust-lang/miri,rust-lang/miri