Without this, a `#include <float.h>` resolves incorrectly. Either the
headers weren't on the include path at all, or they only were for
local, not system, imports.
What's weird is this used to not be a problem. Not sure what other
change in e.g. cc-wrapper would affect this.
I think it's ok to export things which aren't wrapped. The cc-wrapper
can be thought of as responsible for all of binutils and the c
compiler, only wrapping those binaries which are necessary to
interposition---as opposed to all binaries it thinks are relevaant.
Conversely, adding the setup hook to the unwrapped compilers would be
unforunate as hooks are ugly hacks and the compilers themselves take
a long time to rebuild. Better to wholely separate "pure packages" from
hacks.
Packages get --host and --target by default, but can explicitly request
any subset to be passed as needed. See docs for more info.
rustc: Avoid hash breakage by using the old (ignored)
dontSetConfigureCross when not cross building
Eventually we should avoid this "pre-wrapping" and just update those
files in nixpkgs. This mass-rebuild change is best done along with
those needed to reduce the disparity between native and cross (i.e.
making native the "identity cross").
We now (on cross) require per-target flag interposition by putting the
triple in the names of the relevant environment variables, e.g:
export NIX_arm_unknown_linux_gnu_CFLAGS_COMPILE=...
The wrapper also has a `infixSalt` attribute (and "_" prefixed and
suffixed variants) to assist downstream packages.
Note how that the dashes are replaced to keep the identifier valid.
Using names like this allows us to keep the settings for different
compilers seperate.
I think it might be even better to use names like `NIX_{BUILD,HOST}...`
using the platform's role rather than the platform itself, but this
would be more work as the previous stages' tools would have to be re-
wrapped to take on their new role. I therefore didn't do this for now,
but that route should be thoroughly explored in the future.
