[flang-commits] [flang] [flang][Evaluate] Add `ExtractSubstring` to evaluate/tools.h (PR #81265)

[Krzysztof Parzyszek via flang-commits]

kparzysz wrote:

The use case is in an upcoming PR.  I wanted to split things into smaller pieces and this looked general enough to exist on its own...

https://github.com/llvm/llvm-project/pull/81265