LLVM: Bump commit.
librustc: Ignore warnings about debug metadata versions while processing linked archives.
Mk: Fix an issue wherein jemalloc's configure was causing our make to think it
needed to rebuild jemalloc by writing to VERSION in src/jemalloc/.
librustc: Apparently, libc++ contains duplicate file names. So, rename duplicate
files so we don't accidentally delete symbols.
mk/tests.mk: Fixes for handling target specific disabled crates.