I stumbled over a new FAIL (regression) in sollve_vv today, which was due to an
odd corner case (see commit log for a description).

The mentioned in-scan error is tested for in gomp/loop-2.f90 ("'inscan' REDUCTION
clause on construct other than DO, SIMD, DO SIMD, PARALLEL DO, PARALLEL DO SIMD").

I hope that this patch covers all cases and no other surprises exist...

OK for mainline?

  * * *

The ICE is new in GCC 13 due to the duplicate diagnostic (cf. PR); the original issue
existed before but seemingly did not affect the code, at least the sollve_vv testcase
passed before.

Still, it could be backported to GCC 12. (Fortran '!$omp loop' support was added with r12-1206.)
Thoughts?

Tobias
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