Seems that GCC ARM Embedded have changed convention for file location,
and version 5.2 isn't accessible from the predicted url. That's why
nix-expression is updated to allow overloading url parts.
The $lib output refers to the terminfo database in $out, which is about
10x larger than the ncurses shared library. Splitting these outputs
saves a small amount of space for any derivations that use the terminfo
database but not the ncurses library, but we do not have evidence that
any such exist.
Fixes this:
$ arm-none-eabi-gdb
arm-none-eabi-gdb: error while loading shared libraries: libncurses.so.5: cannot open shared object file: No such file or directory
These are packages for precompiled ARM microcontroller compilers from
https://launchpad.net/gcc-arm-embedded.
[Bjørn: modify commit message (add paragraph).]
