Watcom watcall support

[tomsons26]

I've been using a custom ldef and cspec to work with Watcom binaries in Ghidra for a while now, i have no clue how proper these settings are hence it hasn't been mentioned on Ghidra's issues. This seems out of my scope to figure out fully let alone make a PR for Ghidra.

Since Rizin supports watcall (shown as watcom) calling convention seems like this is the best place to bring this up and hopefully maybe get it merged into Ghidra itself too.

These are my spec files as a Ghidra plugin, they work fairly well, except Ghidra assumes everything is a watcall including cdecl when installed. There are some issues where something appears to be detached (spoiled register as i understand?), but these issues appear in IDA as well so it just seems like a watcall quark. (uploaded with txt cause github doesn't allow zip for some reason....)

watcall.zip.txt