Mod poly and mpn_mod random generation #3638

Job	Run time
Ubuntu GCC, Code Coverage (x10)	3h 42m 16s
GCC build regression check (no tests)	1m 7s
Ubuntu GCC with NTL and checking msolve (assert, x2)	3h 42m 15s
Nemo.jl	20m 41s
Ubuntu ARM (x5)	1s
Ubuntu Clang, BLAS and examples (x5)	3h 42m 15s
macOS-M1, Clang (x3)	3h 42m 8s
MinGW GCC (x0.5)	3h 42m 11s
MSVC (x1)	36m 9s
Alpine Linux, musl, 32-bit (assert, x1.5)	3h 42m 16s
	23h 11m 19s

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