*_WRKSRC handling improvements

[AMDmi3]

Summary

There are two features I'd like to improve in *_WRKSRC handling.

1. Currently

CONFIGURE_WRKSRC= ${WRKSRC}
BUILD_WRKSRC= ${WRKSRC}
INSTALL_WRKSRC= ${WRKSRC}

while it's better to chain them:

CONFIGURE_WRKSRC= ${WRKSRC}
BUILD_WRKSRC= ${BUILD_WRKSRC}
INSTALL_WRKSRC= ${INSTALL_WRKSRC}

as if CONFIGURE_WRKSRC changes, it's probable BUILD_WRKSRC will be changes in the same way. The same for INSTALL_WRKSRC.

Most ports have to change all three directories, there are 144 cases of _WRKSRC=.*_WRKSRC in the portstree.

This makes *_WRKSRC handling more consistent with some Uses/*, as cmake.mk and qmake.mk already use this scheme.

2. Make it possible to stick multiple values into {CONFIGURE,BUILD,INSTALL}_WRKSRC

This idea came to me while investigating problem with devel/tex-web2c: it calls additional configure but doesn't pass CC/CXX/CFLAGS/... to it, as these are not passed via CONFIGURE_ENV

There are at least 16 cases in the portstree where additional configures are called.

Note that this is not a complete patch yet, but just a demonstartion of the idea. While (2) is probably no-op now, (1) requres changing some ports which rely on an old logic. If the idea is approved I'll process these ports as well

[bdrewery]

I'm confused on this. I at first was fine with the idea of chaining them, assuming ports were going to need less code after that. There's no port examples though.

I'm confused why we need to support multiple directories like this. Nothing seems improved in this patch; There's more code added than removed in all touched places.

Perhaps I need to see some specific port examples where this cleanup is a benefit.

[bapt]

I agree with @bdrewery here please elaborate a bit :)