fix: aarch64 is not supported, should set ARCH to RELIC_NONE #383

Job	Run time
macos-latest, cmake, gcc, easy backend	43s
macos-latest, cmake, gcc, gmp backend	36s
macos-latest, cmake, clang, easy backend	31s
macos-latest, cmake, clang, gmp backend	35s
macos-latest, autotools, gcc, easy backend	1m 3s
macos-latest, autotools, gcc, gmp backend	1m 1s
macos-latest, autotools, clang, easy backend	1m 4s
macos-latest, autotools, clang, gmp backend	57s
ubuntu-20.04, cmake, gcc, easy backend	1m 32s
ubuntu-20.04, cmake, gcc, gmp backend	1m 30s
ubuntu-20.04, cmake, clang, easy backend	1m 34s
ubuntu-20.04, cmake, clang, gmp backend	1m 26s
ubuntu-20.04, autotools, gcc, easy backend	2m 18s
ubuntu-20.04, autotools, gcc, gmp backend	2m 7s
ubuntu-20.04, autotools, clang, easy backend	2m 10s
ubuntu-20.04, autotools, clang, gmp backend	1m 54s
	21m 1s

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