Check availability of rbit instruction #3179

Job	Run time
Alpine Linux, musl, 32-bit (assert, x1.5)	14m 11s
GCC build regression check (no tests)	1m 3s
macOS-M1, Clang (x3)	11m 46s
MinGW GCC (x0.5)	10m 58s
MSVC (x1)	9m 50s
Nemo.jl	18m 17s
Ubuntu ARM (x5)	12m 24s
Ubuntu Clang, BLAS and examples (x5)	12m 37s
Ubuntu GCC, Code Coverage (x10)	30m 52s
Ubuntu GCC with NTL (assert, x2)	8m 7s
	2h 10m 5s

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