Add support for clang-cl on Windows #213

Job	Run time
host-win-msvc	1m 52s
coding-style	15s
host-win (x86_64)	53s
host-arm (armv7, none, none, g++-10)	3m 11s
host-win (armv7)	52s
host-arm (armv7, none, none, clang++-11)	3m 31s
host-win (aarch64)	43s
host-arm (aarch64, none, none, g++-10)	2m 45s
host-x86 (x86_64, g++-10)	1m 58s
host-arm (aarch64, none, none, clang++-11)	3m 24s
host-x86 (x86_64, clang++-11)	18s
host-arm (aarch64, crypto+crc, none, g++-10)	2m 52s
host-arm (aarch64, crypto+crc, none, clang++-11)	3m 36s
host-arm (armv7, none, -mcpu=cortex-a32 -mfpu=neon-fp-armv8, g++-10)	3m 13s
host-arm (armv7, none, -mcpu=cortex-a32 -mfpu=neon-fp-armv8, clang++-11)	3m 33s
test-win-msvc	48s
	33m 44s

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