When building math/openblas, it fails to build due to CPU detection failure:
===> Building for openblas-0.2.20_3,1
cd /construction/xports/math/openblas/work/OpenBLAS-0.2.20 ; /usr/bin/env BINARY64=1 DYNAMIC_ARCH=1 NO_AVX=1 NO_AVX2=1 NUM_THREADS=1 USE_THREAD=0 gmake DESTDIR=/construction/xports/math/openblas/work/stage
gmake: Entering directory '/construction/xports/math/openblas/work/OpenBLAS-0.2.20'
Makefile:128: *** OpenBLAS: Detecting CPU failed. Please set TARGET explicitly, e.g. make TARGET=your_cpu_target. Please read README for the detail.. Stop.
gmake: Leaving directory '/construction/xports/math/openblas/work/OpenBLAS-0.2.20'
*** Error code 2
Note that DYNAMIC_ARCH=1, and this is not a manual build! The problem is that the port assumes that this flag disables CPU detection in OpenBLAS build, but it actually doesn't; see https://github.com/xianyi/OpenBLAS/issues/1024. It seems that the only workaround is to explicitly specify some reasonable baseline CPU with TARGET= - this will allow the build do proceed, but shouldn't matter for the resulting binaries due to DYNAMIC_ARCH being set.
This will not repro on those machines for which CPU type is known by OpenBLAS, since CPU detection succeeds there - this is likely the reason why it doesn't show up in official package builds. In my case, the machine is a Lenovo Thinkpad 11e with Celeron N2940 CPU.
Maintainer feedback, please!