POSIX added these GNU extensions for issue 8.
I've made these always inline without the usual "until API level X"
proviso because they're single instructions that the compiler can inline
and there's really no point providing these if they add function call
overhead --- everyone should just use __builtin_ffs() and friends
instead in that case.
Bug: https://austingroupbugs.net/view.php?id=617
Test: treehugger
Change-Id: I33fc4b8648ea25917329e81c1b4c60eb9a66d667
4a6899ce0c