Add support for cross compiling to the rump kernel

[posix4e]

https://github.com/rumpkernel/ is a neat project for a minimal netbsd anykernel. Since rump kernel is compatible with netbsd I've started adding support for cross compiling a amd64 netbsd rustc at
#26682
rust-lang/rust-installer#38

An additional pull request needs to be filed actually get rust to use that rust-installer pull request. Once netbsd is in the tree, compiling for rump should be trivial.

[posix4e]

For some reason I can't assign this to myself

[Gankra]

Only members of the organization can be assigned an issue.

[posix4e]

Gatcha! cheers

[posix4e]

So we got the first two pull requests in, now we need to build a stage0 snapshot

fetch: x86_64-unknown-netbsd/stage0/bin/rustc
Traceback (most recent call last):
File "/root/rust/src/etc/get-snapshot.py", line 78, in
main(sys.argv)
File "/root/rust/src/etc/get-snapshot.py", line 60, in main
snap = determine_curr_snapshot(triple)
File "/root/rust/src/etc/snapshot.py", line 301, in determine_curr_snapshot
(platform, rev))
Exception: no snapshot file found for platform netbsd-x86_64, rev 7b95b5c
/root/rust/mk/stage0.mk:17: recipe for target 'x86_64-unknown-netbsd/stage0/bin/rustc' failed
gmake: *** [x86_64-unknown-netbsd/stage0/bin/rustc] Error 1

I'm curious if this is something I can do. I certainly can cross compile one on linux

[alexcrichton]

Done! The x86_64-rumprun-netbsd target is suitable for this