Allow enabling/disabling the Watcom "GUI" components

I would like to compile only the compiler and linker without having to drag out dosemu/dosbox for GUI components that I never use. In the setvars.sh example the variable is set to 1 by default so that the build-time behavior remains unchanged for those who want the GUI browser WGML headers as normal.

I am not sure how to specify to Github how to create a pull request for only a specific range of commits. The net effect is that only the last 3 commits change anything. The changes to create the win32s target have been rolled back and "win32s" uses the same CLIB as the "nt" target as it did before. Please cherry-pick if necessary all commits after "bring my main branch up to match the project".

I configured DOSLIB to use the -s switch to disable stack checking for win32s targets. Binaries work perfectly fine now in Windows 3.1 when Win32s v1.20 and later are installed.