[flang] Add support of sanitizers

At the current moment, flang does not support:

- [ ] AddressSanitizer: https://godbolt.org/z/K5dKxYEnb
- [ ] LeakSanitizer: https://godbolt.org/z/s1nWfjYjh
- [ ] MemorySanitizer: https://godbolt.org/z/7674EK3a7
- [ ] UndefinedSanitizer: https://godbolt.org/z/nP6dPbMsE
- [ ] ThreadSanitizer: https://godbolt.org/z/GTKM3c5Tf

It would be nice to see their support with flang.

Hope I mentioned all available sanitizers in LLVM.

Start by running the five linked Godbolt examples with flang and compare the current behavior for AddressSanitizer, LeakSanitizer, MemorySanitizer, UndefinedSanitizer, and ThreadSanitizer. Done means flang supports the sanitizers listed in the issue, with behavior that can be demonstrated for each example.

Written by the indexing model from the issue text.