Allow optimization and use fesetround(), fegetround() #283

Job	Run time
coding-style	13s
host-win (x86_64)	51s
host-arm (armv7, none, none, g++-10)	5m 46s
host-win-msvc	47s
host-win (armv7)	58s
host-arm (armv7, none, none, clang++-11)	5m 48s
host-win (aarch64)	52s
host-arm (aarch64, none, none, g++-10)	5m 47s
host-x86 (x86_64, g++-10)	1m 1s
host-arm (aarch64, none, none, clang++-11)	5m 45s
host-x86 (x86_64, clang++-11)	48s
host-arm (aarch64, crypto+crc, none, g++-10)	5m 48s
host-arm (aarch64, crypto+crc, none, clang++-11)	5m 44s
host-arm (armv7, none, -mcpu=cortex-a32 -mfpu=neon-fp-armv8, g++-10)	5m 47s
host-arm (armv7, none, -mcpu=cortex-a32 -mfpu=neon-fp-armv8, clang++-11)	5m 47s
test-win-msvc	44s
	52m 26s

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