dev-rust/const_fn: Add new crate for conditionally making functions const.

This crate appears to recent and quickly rising in popularity as
people make libs aware of the new const fn support in the compiler,
and it's used by current crossbeam.  I've done a quick sanity check of
the github and things look reasonable.

TEST=emerge-trogdor deqp-runner

Change-Id: Ifb0b5110373e58238cb84c783474a822c45ad996
Tested-by: Eric Anholt <>
Reviewed-by: Eric Anholt <>
Reviewed-by: Chirantan Ekbote <>
Commit-Queue: Eric Anholt <>
2 files changed