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Add support for _mm256_blendv_epi8 #638

Job	Run time
Dub Tests (windows-latest, dmd-latest)	46s
Dub Tests (windows-latest, dmd-2.097.0)	35s
Dub Tests (windows-latest, dmd-2.096.1)	36s
Dub Tests (windows-latest, dmd-2.095.1)	28s
Dub Tests (windows-latest, dmd-2.094.2)	30s
Dub Tests (windows-latest, ldc-latest)	47s
Dub Tests (windows-latest, ldc-1.33.0)	41s
Dub Tests (windows-latest, ldc-1.32.2)	40s
Dub Tests (windows-latest, ldc-1.31.0)	48s
Dub Tests (windows-latest, ldc-1.30.0)	43s
Dub Tests (windows-latest, ldc-1.29.0)	41s
Dub Tests (windows-latest, ldc-1.28.1)	45s
Dub Tests (windows-latest, ldc-1.27.1)	43s
Dub Tests (windows-latest, ldc-1.26.0)	48s
Dub Tests (windows-latest, ldc-1.25.1)	45s
Dub Tests (windows-latest, ldc-1.24.0)	43s
	10m 59s

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