Add compiler:c++11-lang to USES to fix build on GCC-based systems:
/wrkdirs/usr/ports/math/py-qdldl/work-py37/qdldl-0.1.5.post0/c/amd/src/perm.c:23: error: 'for' loop initial declaration used outside C99 mode cc1plus: error: unrecognized command line option "-std=c++11"
Approved by: portmgr (tier-2 blanket)