with structuredAttrs lists will be bash arrays which cannot be exported
which will be a issue with some patches and some wrappers like cc-wrapper
this makes it clearer that NIX_CFLAGS_COMPILE must be a string as lists
in env cause a eval failure
With all libcs I'm aware of, libdl is now either empty (Glibc, musl,
uclibc, illumos), a symlink to libc or equivalent (Apple), or does not
exist (FreeBSD, NetBSD). So explicitly linking libdl now does nothing
for the former platforms, and breaks the build for the latter
platforms.
With this patch I've removed -ldl from all overridden linker flags for
all free packages in Nixpkgs. Everything still seems to build.
We revert to using GCC 9 for compilation, in order to work around a GCC 10 bug
resulting in a segfault when compiling.
The alternative would be to restrict to optimization level -O1, but this
disables fortify.
