If e.g. -march=haswell is set in CFLAGS, GCC generates FMAs by default, which
is inconsistent with the microkernels, none of which use FMAs. These
inconsistencies cause a few failures in the LAPACK testcases, where
eigenvalue results with/without eigenvectors are compared.
Moreover using FMAs for multiplication of complex numbers can give surprising
results, see 22aa81f for more information.
This uses the same syntax as used in 22aa81f for zarch (s390x).
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