Add support for arm64ec #852

Job	Run time
iOS (aarch64-apple-ios, iphoneos)	30s
iOS (x86_64-apple-ios, iphonesimulator)	24s
Test (ubuntu-20.04, stable)	2m 17s
Windows AArch64	1m 52s
Test (ubuntu-20.04, beta)	1m 50s
Test (ubuntu-20.04, nightly)	2m 16s
Build Targets (wasm32-unknown-unknown)	19s
Test (macos-latest, stable)	2m 23s
Build Targets (wasm32-wasi)	18s
Test (macos-latest, nightly)	3m 12s
Docker (aarch64-unknown-linux-gnu)	1m 0s
Build Targets (x86_64-unknown-fuchsia)	20s
Miri	1m 57s
Test (windows-latest, stable-x86_64-msvc)	2m 59s
Docker (arm-unknown-linux-gnueabihf)	56s
Build Targets (x86_64-fortanix-unknown-sgx)	17s
Test (windows-latest, stable-i686-msvc)	2m 14s
Docker (armv7-unknown-linux-gnueabihf)	37s
Build Targets (x86_64-unknown-illumos)	18s
Test (windows-latest, stable-x86_64-gnu)	2m 39s
Docker (i586-unknown-linux-gnu)	43s
MSRV	3m 26s
Docker (i686-unknown-linux-gnu)	46s
Rustfmt	11s
Docker (powerpc64-unknown-linux-gnu)	1m 3s
Docker (s390x-unknown-linux-gnu)	46s
Docker (x86_64-pc-windows-gnu)	47s
Docker (x86_64-unknown-linux-gnu)	42s
Docker (x86_64-unknown-linux-musl)	49s
Docker (arm-linux-androideabi)	1m 28s
Docker (armv7-linux-androideabi)	1m 46s
Docker (aarch64-linux-android)	1m 54s
Docker (i686-linux-android)	1m 27s
Docker (x86_64-linux-android)	1m 18s
	45m 44s

Provide feedback