[llvm-branch-commits] [flang][runtime] Added self-printing for InternalUnit. (PR #85181)

[Slava Zakharin via llvm-branch-commits]

https://github.com/vzakhari created https://github.com/llvm/llvm-project/pull/85181

An InternalUnit might be constructed to allocate its own "output"
buffer of a predefined size. The buffer is then used for collecting
all the output, and it printed by std::printf at the end of the statement.

This is a suggested way for supporting 'PRINT *, ...' in the device code.
It might be not ideal, because the output is not formatted the same way
as the UNIT=5 output is formatted by default.