Bug#961725: libopenblas-dev: On some cpus, openmp and pthread dead-lock

[Mo Zhou]

> Just one question: did you try to rebuild it from source without
> changing anything? Maybe it’s just the rebuild that fixed it, and not
> the flag change.

Rebuilt without change: hang with libopenblas0-pthread

Rebuilt with USE_TLS=0: hang

Rebuilt with USE_SIMPLE_THREADED_LEVEL3=1: hang

Rebuilt with "-Wl,-Bsymbolic-functions" stripped: pass