reason for both --libdir and --libsubdir ?

[Duncan Coutts]

I am trying to understand the reason we have so many --dir flags to
configure. I'd prefer to remove what appear to be duplicates and add
some more dir overrides for specific file types (like docs).

We currently have:

--libdir= and --libsubdir=
--datadir= and --datasubdir=

in each case the subdir flavour is an extra directory underneath the
main dir which defaults to the package id. Seems to me that we can get
rid of the subdir stuff because you can say:

--libdir='/foo/bar/$pkgid/$compiler'

Indeed this already works. So can we deprecate the subdir variants and
tell people to just use these vars?

The only thing the subdir thing was for is to be able to adjust the
libdir while still getting the pkgid and compiler components generically
and we can do that more flexibly with vars.

Duncan