We're making lapack rely on OpenBLAS's implementaiton of BLAS...
and the latter already provides its own "cblas".
Unless we make the _devel package conflict with one another,
we better disable cblas here.
Also: `lapack.pc` still referenced a "blas" .pc file (as would be the case
if we wre using the lapack-provided BLAS).
Changing that to point to openblas.pc instead fixes the meson-based build of
`scipy` (and with no missing symbols at runtime).
Fixes#11784.
Moved cmd:python3 to TEST_REQUIRES, as even if it seems like the
build needs it (for "summary tests"), it actually doesn't, and its
only for "make test" we need Python3.
Added $jobArgs, as that speeds up the build quite a lot.
Testes passed 100% with or without that set, in any case.
x86_64 is used as a baseline: the "x86_64" entry, whatever status it has,
is transformed into "all", and then the other entries in ARCHITECTURES
either dropped or rearranged appropriately.
