Allow optimization and use fesetround(), fegetround() #302

Job	Run time
host-arm (armv7, none, none, g++-10)	4m 42s
host-win-msvc	1m 4s
host-arm (armv7, none, none, clang++-11)	3m 40s
host-arm (aarch64, none, none, g++-10)	2m 52s
host-win (x86_64)	44s
host-x86 (x86_64, g++-10)	2m 0s
host-arm (aarch64, none, none, clang++-11)	3m 38s
coding-style	16s
host-win (armv7)	54s
host-x86 (x86_64, clang++-11)	20s
host-arm (aarch64, crypto+crc, none, g++-10)	2m 47s
host-win (aarch64)	41s
host-arm (aarch64, crypto+crc, none, clang++-11)	3m 53s
host-arm (armv7, none, -mcpu=cortex-a32 -mfpu=neon-fp-armv8, g++-10)	3m 15s
host-arm (armv7, none, -mcpu=cortex-a32 -mfpu=neon-fp-armv8, clang++-11)	3m 50s
test-win-msvc	56s
	35m 32s

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