Added support to build under MSYS2 environment
* Automatically setup build environment for MSYS2 if
C:\MSYS64 is present and lean.
* Fixed `checkout_svn` to work with MSYS2 version of SubVersion.
For some reason that version of `svn.exe` does not like Windows
absolute filenames starting with 'device letter'. In that case
the actually directory for checkout is messed up. To workaround,
always use relative paths when specifying workiing copy path
* Added Borland's `make.exe` to `bin` as Smalltalk/X Windows makefiles
still uses it. Triple sigh here.
(binary:application/x-msdos-program)