[Omake] Cygwin toolchain using standard win32 install

[Andrew Gacek]

> Note that as long as you set OSTYPE before opening any files (including
> build/Common and build/C), then you do not need to also mess with
> GCC_FOUND/YACC/LEX/EXE/etc - as long as you set OSTYPE early enough, all
> those will follow automatically.

Right now I have

  if $(equal $(OSTYPE), Win32)
    OSTYPE = Cygwin
    GCC_FOUND = true
    GXX_FOUND = true
    export

as the very first lines in my OMakeroot file. After these lines I open
build/C and build/OCaml. But if I leave out the GCC_FOUND = true I
get,

  *** omake: reading OMakefiles
  *** omake error:
     File c:\Program Files\OMake\lib\omake\\build\C.om: line 96,
characters 21-33
     unbound variable: GCC_FOUND

-Andrew