Install msys from

Note this is only msys, not msys+mingw since we are not using gcc
Uncompress into (e.g.) c:\msys

Notes:
* Use forward / in paths to configure
* At the moment, Tcl only builds in the TCLSRC/win and TKSRC/win directories
* If doing 64-bit builds, add --enable-64bit

Use "Developer Command Prompt" from MSVC, not msys sh. For ./configure to run, you need to add
to your path:

set
set CC=cl.exe
cd PATH_TO_TCLSRC\win
sh configure  --prefix=TCL_INSTALL_DIR --enable-threads
make
make install
cd PATH_TO_TKSRC\win
sh configure  --prefix=TCL_INSTALL_DIR --enable-threads
make
make install