Support larger machines with OpenBLAS

[eschnett]

Julia's deps/Makefile contains these lines:

# On linux, try to provision for the largest possible machine currently
OPENBLAS_BUILD_OPTS += NUM_THREADS=16

We have a system with 28 cores, and larger systems exist. Should this limit be increased?

[yuyichao]

Maybe ref OpenMathLib/OpenBLAS#103

[andreasnoack]

It would be great to be able to set this with variable in Make.user.

[Keno]

The comment is misleading. @vtjnash explained what this number actually is in JuliaLang/julia#14857

[eschnett]

@vtjnash Can you suggest a better formulation for this comment?

[ViralBShah]

The only way is to try this out, but we want a small default also for memory allocation reasons.

[ViralBShah]

Increasing this limit severely increases the amount of memory as @vtjnash mentions in JuliaLang/julia#14857 (comment)

Thus, it is unlikely the defaults will change unless upstream does something about it.