Fix AVX detection #157

Job	Run time
makefile-analysis	46s
cmake-alpine-amd64-gcc	17s
makefile-ubuntu-20.04-amd64-gcc	6s
makefile-ubuntu-20.04-amd64-gcc +openmp	6s
makefile-alpine-armv7-gcc	1m 31s
cmake-alpine-armv7-gcc	1m 57s
makefile-alpine-amd64-gcc	13s
makefile-ubuntu-20.04-amd64-clang	7s
makefile-alpine-armv7-clang	1m 56s
cmake-alpine-armv7-clang	1m 29s
makefile-ubuntu-20.04-amd64-clang +openmp	4s
makefile-alpine-aarch64-gcc	1m 37s
makefile-macos-11-amd64-clang	15s
makefile-alpine-aarch64-clang	1m 20s
cmake-ubuntu-20.04-x86_64	9s
makefile-alpine-s390x-gcc	1m 42s
cmake-ubuntu-20.04-i686	44s
makefile-alpine-s390x-clang	2m 14s
cmake-macos-11-x86_64	18s
makefile-alpine-ppc64le-gcc	1m 0s
cmake-alpine-aarch64-gcc	1m 17s
cmake-windows-2019-x86_64	49s
makefile-alpine-ppc64le-clang	1m 26s
cmake-alpine-aarch64-clang	1m 39s
cmake-windows-2019-i686	1m 2s
cmake-alpine-s390x-gcc	1m 21s
cmake-alpine-s390x-clang	2m 53s
cmake-alpine-ppc64le-gcc	1m 39s
cmake-alpine-ppc64le-clang	1m 34s
	31m 31s

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