Fixes#177501
This PR fixes a compilation crash when using character types in OpenMP
REDUCTION clauses with declare_reduction directives.
The problem was that character types weren't being handled properly
during OpenMP lowering. Specifically:
- Missing character length parameters in hlfir.declare operations
- Incorrect type wrapping for by-ref reductions
- Missing special case handling for boxed/unboxed character types
The fix ensures character types are treated similarly to derived types
throughout the reduction pipeline, since fir::isa_trivial() excludes
them.
Added a regression test to verify the fix works for both allocatable and
non-allocatable character reductions.
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