Attempted fix for errors observed on:
https://luci-milo.appspot.com/ui/p/fuchsia/builders/toolchain.ci/clang-windows-x64/b8724466517233166081/overview

Following the previous fixes, one test that needed an explicit triple
was missed; this commit adds that triple.

Following the previous patch which adds the "extend lifetimes" flag
without (almost) any functionality, this patch adds the real feature by
allowing Clang to emit fake uses. These are emitted as a new form of cleanup,
set for variable addresses, which just emits a fake use intrinsic when the
variable falls out of scope. The code for achieving this is simple, with most
of the logic centered on determining whether to emit a fake use for a given
address, and on ensuring that fake uses are ignored in a few cases.

Co-authored-by: Stephen Tozer <stephen.tozer@sony.com>