Change the meaning of NO_WRKSUBDIR to force a WRKDIR != WRKSRC.
Right now, NO_WRKSUBDIR means that the extraction does not produce a
subdirectory, and that everything goes straight into WRKDIR. It is
problematic, because during the build of a port, quite a few files are
created in there, and then, a stage directory, where everything is
installed, and then a pkg directory where the package is created, and
those often conflict, or get in the way, of the building process.
With this, NO_WRKSUBDIR will extract the distfiles directly into WRKSRC
instead of WRKDIR. In this case, WRKSRC is artificial and is based on
PKGNAME and not DISTNAME, mitigate conflicts with rc files.