This is especially useful when not cross compiling. It means we can
remove the `stdenv.isGlibc` predicate too.
Additionally, use this to simplify the logic to choose the
appropriate libiconv derivation.
This reverts commit 2282a5774c, reversing
changes made to 14adea9156.
The lib tests are bloking nixpkgs-unstable, and I don't like debugging
it soon enough.
There is no more `cygwin` OS, but instead a `cygnus` abi. "win32"
and "mingw32" parse as `windows`. Add a 3-part hack because autotools
breaks on explicit abi with windows-like (e.g. "i686-pc-windows-gnu").
Also change cross triples to conform
The old hard-coded lists are now used to test system parsing.
In the process, make an `assertTrue` in release lib for eval tests; also
use it in release-cross
