games/chromium-bsu: Respect LDFLAGS and let LLD_UNSAFE actually work

/usr/bin/ld: error: cannot preempt symbol: alcOpenDevice

defined in /usr/local/lib/libopenal.so
referenced by AudioOpenAL.cpp

chromium_bsu-AudioOpenAL.o:(AudioOpenAL::AudioOpenAL())

http://beefy12.nyi.freebsd.org/data/head-amd64-default/p474767_s336359/logs/chromium-bsu-0.9.16.1_1.log

PR: 226980
Reported by: emaste, pkg-fallout