Patch clang _mul_ppmm to work with (s|u)div_qrnnd #1627

Job	Run time
macOS-M1, Clang (x3)	6m 18s
Ubuntu GCC, Code Coverage (x10)	30m 57s
Alpine Linux, musl, 32-bit (assert, x1.5)	14m 12s
GCC build regression check (no tests)	1m 11s
MinGW GCC (x0.5)	10m 31s
MSVC (x1)	10m 18s
Nemo.jl	18m 29s
Ubuntu Clang, BLAS and examples (x5)	4m 1s
Ubuntu GCC with NTL (assert, x2)	9m 30s
	1h 45m 27s

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