[PATCH 6/8] Add support for the Rust language

[Tom Tromey]

>>> +  /* Rust does not currently emit DW_LANG_Rust or DW_LANG_Rust_old.
Pedro> "Currently" is a moving target.  Could you replace it with some
Pedro> version number or some such?

Tom> It turns out that the patch to drop DW_LANG_Rust didn't go in yet, since
Tom> it causes an assertion failure in LLVM.  This will probably shake out
Tom> before the copyright assignments are done anyway.

I'm thinking I will just drop this hunk.  Even if the patch does go in
soon, it will only be in nightly, and that's known not to work yet for
other reasons -- and since other changes might need to be done at some
point for nightly, we can always restore this producer sniffing stuff
later as well.

Tom