ICU-21374 Add a CFI build bot for ICU4C

[erik0686]

Checklist

• [x] Required: Issue filed: https://unicode-org.atlassian.net/browse/ICU-21374
• [x] Required: The PR title must be prefixed with a JIRA Issue number.
• [x] Required: The PR description must include the link to the Jira Issue, for example by completing the URL in the first checklist item
• [ ] Required: Each commit message must be prefixed with a JIRA Issue number.
• [x] Issue accepted (done by Technical Committee after discussion)
• [ ] Tests included, if applicable
• [ ] API docs and/or User Guide docs changed or added, if applicable

[FrankYFTang]

How about we also add -fno-sanitize-trap=all and -fsanitize-recover=

see https://blog.fuzzing-project.org/57-Diving-into-Control-Flow-Integrity.html

[markusicu]

Progress? Assignee? Reviewers? @erik0686 @jefgen @rp9-next @gnrunge

[rp9-next]

I checked with @erik0686 on this. It seems, enabling the bot opened gates for potential issues in ICU code that may have to be re-investigated.

Considering the time gap, the build bot might also need to be re-done.

It seems @FrankYFTang was interested in helping last time. Maybe we can start working on it post 72.

[markusicu]

@FrankYFTang & @rp9-next please try to move this forward.

[FrankYFTang]

Move the content of this PR to https://github.com/unicode-org/icu/pull/2284 since I cannot push into https://github.com/erik0686/icu/tree/cfi-buildbot