Reapply "DebugInfo: Ensure that all debug location scope chains from instructions within a function, lead to the function itself."

Originally reverted in r213432 with flakey failures on an ASan self-host
build. After reduction it seems to be the same issue fixed in r213805
(ArgPromo + DebugInfo: Handle updating debug info over multiple
applications of argument promotion) and r213952 (by having
LiveDebugVariables strip dbg_value intrinsics in functions that are not
described by debug info). Though I cannot explain why this failure was
flakey...

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@214761 91177308-0d34-0410-b5e6-96231b3b80d8
Add a sentence that all entries should include an email address.
Add one for Greg Clayton, Peter Collingbourne, Tobias Grosser and
Jakob Olesen based on recent commits.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@214762 91177308-0d34-0410-b5e6-96231b3b80d8