configure: Add MINGW64 OS type

MSYS2 supports `MINGW64` system for 64-bit environment. It sets
`MSYSTEM=MINGW64` environment variable, which changes output of
`uname -s` thus affects `configure` behavior.

This patch adds `MINGW64*` support for `configure`.
auto merge of #13199 : klutzy/rust/msys2, r=cmr

MSYS2 supports `MINGW64` system for 64-bit environment. It sets
`MSYSTEM=MINGW64` environment variable, which changes output of
`uname -s` thus affects `configure` behavior.

This patch adds `MINGW64*` support for `configure`.