Auto merge of #39837 - alexcrichton:llvm-crt-static, r=brson
rustc: Link statically to the MSVCRT
This commit changes all MSVC rustc binaries to be compiled with
`-C target-feature=+crt-static` to link statically against the MSVCRT instead of
dynamically (as it does today). This also necessitates compiling LLVM in a
different fashion, ensuring it's compiled with `/MT` instead of `/MD`.
cc #37406