Bundled libmingwex.a doesn't contain strtok_r

[kryptan]

libmingwex.a which is installed with *-pc-windows-gnu toolchains doesn't contain implementation of strtok_r. This and other mingw libraries are probably outdated. The latest version in mingw-w64 does contain strtok_r. This causes issues when linking with libcurl. I think all mingw libraries should be updated to the latest version.

I don't know if this is the right repo for this issue as I don't know where is the build script which builds mingw libraries shipped by rustup.

[Diggsey]

This should be reported to rust-lang/rust if it's still an issue.