compiler: Fix parlang reductions over >= 4 loops #6847

Job	Run time
pytest-ubuntu-py311-gcc11-noomp-base	38m 15s
pytest-ubuntu-py311-gcc11-noomp-adjoint	32m 43s
pytest-ubuntu-py38-gcc12-omp-base	40m 42s
pytest-ubuntu-py38-gcc12-omp-adjoint	34m 32s
pytest-ubuntu-py38-gcc7-omp-base	41m 0s
pytest-ubuntu-py38-gcc7-omp-adjoint	35m 8s
pytest-ubuntu-py310-gcc10-noomp-base	37m 20s
pytest-ubuntu-py310-gcc10-noomp-adjoint	32m 37s
pytest-ubuntu-py312-gcc13-omp-base	50m 9s
pytest-ubuntu-py312-gcc13-omp-adjoint	41m 34s
pytest-ubuntu-py39-gcc9-omp-base	39m 6s
pytest-ubuntu-py39-gcc9-omp-adjoint	33m 9s
pytest-osx-py312-clang-omp-base	1m 37s
pytest-docker-py39-gcc-omp-base	39m 34s
pytest-docker-py39-gcc-omp-adjoint	29m 35s
pytest-docker-py39-icx-omp-base	31m 57s
pytest-docker-py39-icx-omp-adjoint	29m 20s
	9h 48m 18s

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