[release.sh] Do not use Microsoft's lib.exe for creation of MSVC import libs.

Instead we just rename libmctrl.a as created with mingw-w64. The import
lib produced by lib.exe had some problems with symbol decorations. Newer
MSVC versions dealt with it anyway, but less tolerant linkers (e.g. MSVC
6) do not.

However every MSVC version seems to be happy with the renamed libmctrl.a.