Use `quick_exit` instead of `_exit` (except for error handling).

Replace every occurrence of `_exit` (for cases other than pure error
handling) with `quick_exit`, in order to allow functions registered
with `at_quick_exit` to be called before exiting.

In particular, this change will allow LLVM's code coverage profile
dumping routine to be called before exiting ART processes.

Test: mmma art
Test: ART tests
Bug: 186576313
Change-Id: Ia9b0dbb471e2a26600c8bd23f7567931d050fc9d
5 files changed