build

Add OpenMP to ext_acc #1061

Job	Run time
ci (Release, linux gnu-10)	18m 47s
ci (Release, linux clang-12)	16m 42s
ci (Release, linux nvhpc-21.9)	14m 55s
ci (Release, linux intel-classic)	13m 34s
ci (Release, macos)	11m 1s
ci (Debug, linux gnu-10)	27m 28s
ci (Debug, linux clang-12)	18m 58s
ci (Debug, linux nvhpc-21.9)	34m 21s
ci (Debug, linux intel-classic)	22m 16s
ci (Debug, macos)	11m 6s
	3h 9m 8s

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