[TCWG-1424] Profile guided information code size investigation. - Wrote up initial findings in Jira - Have written a pass that works with both the new and old pass manager that I can use to selectively add size optimisation attributes to functions. - Spent way too much time trying to work out where to put the pass in both the old and new pass manager. -- I now understand why the new pass manager is required to get the most benefits of profile feedback. -- I now understand a bit better some of the frustrations of the old pass manager. -- I can see why the new pass manager isn't quite ready yet. - Fixed up, I think, -fprofile-instr-generate in the new pass manager. I didn't realise that were two separate instrumentation methods as -fprofile-generate is subtly different.

Misc: - Updated state of sanitizer tests on Arm and AArch64 to enable a PR to be closed.