Changes for fallback SHA-512 and added MacOS CI tests #54

Job	Run time
build_python_ubuntu (x64, gcc, --enable-python)	1m 7s
build_dist (x64, gcc)	1m 35s
build_setup_py_ubuntu (x64, gcc, 3.10)	1m 10s
build_ubuntu (x86, clang)	1m 11s
build_ubuntu (x64, clang)	1m 1s
build_ubuntu (x86, gcc)	58s
coverage_ubuntu (x86, gcc)	52s
build_ubuntu (x64, gcc)	52s
coverage_ubuntu (x64, gcc)	49s
build_ubuntu (x64, gcc, --with-pthread=no)	58s
build_ubuntu (x64, gcc, --with-openssl=no)	1m 9s
build_ubuntu (x64, gcc, --enable-openssl-evp-cipher=yes --enable-openssl-evp-md=yes)	1m 11s
build_ubuntu (x64, gcc, --enable-openssl-evp-cipher=no --enable-openssl-evp-md=no)	53s
build_ubuntu (x64, gcc, --enable-static-executables=yes --enable-multi-threading-support=no)	45s
	14m 31s

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