Windows: Static libraries should end with .lib not .a when using the MSVC ABI install

[pjmlp]

The standard extension for Windows static libraries is .lib.

By keeping the .a extension while using the MSVC ABI, we are forced to rename the files when integrating Rust libraries into compiler chains that expect .lib as an extension.

Reopening the bug here as suggested by alexcrichton (rust-lang/cargo#2100)

[nagisa]

Duplicateish of #28025. Maybe reopen that instead, since it has more discussion?

[retep998]

rustc foo.rs --crate-type=staticlib produces libfoo.a.
This needs to be changed to produce foo.lib for -msvc.

[retep998]

Actually, since that would conflict with the import library produced by --crate-type=dylib I propose using libfoo.lib instead for staticlib as it matches the conventions that Microsoft uses to distinguish static/dynamic libraries (such as ucrt.lib vs libucrt.lib)