Add mutex in feature detection code #209

Job	Run time
build-native-gcc	2m 56s
build-native-llvm	3m 45s
test-native-gcc	7m 49s
build-aarch64-gcc	7m 58s
test-native-llvm	8m 8s
build-aarch64-llvm	6m 53s
build-armhf-gcc	7m 17s
build-armhf-llvm	5m 8s
build-ppc64el-gcc	6m 52s
build-ppc64el-llvm	5m 33s
build-s390x-gcc	6m 8s
build-s390x-llvm	4m 29s
build-riscv64-llvm	6m 43s
test-${{ matrix.arch }}-${{ matrix.compiler }} (qemu_cpu: "${{ matrix.qemu_cpu }}")	0s
	1h 19m 39s

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