Linear algebra tuning for nfloat + cmpabs #2751

Job	Run time
macOS-M1, Clang (x3)	8m 35s
macOS-x86 Clang with BLAS (x2)	14m 19s
GCC build regression check (no tests)	1m 2s
Alpine Linux, musl, 32-bit (assert, x1.5)	13m 31s
MinGW GCC (x0.5)	10m 51s
MSVC (x1)	9m 10s
Nemo.jl (temporary branch)	12m 1s
Ubuntu Clang with examples (x5)	12m 33s
Ubuntu GCC, Code Coverage (x10)	30m 13s
Ubuntu GCC with NTL (assert, x2)	8m 29s
	2h 0m 44s

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