MFH: r399540

• Add a workaround for a problem caused by clang

For some reason clang is breaking the code when openal-soft is built with
optimizations. If the file alBuffer.c is built with -O1 the problem don't
happens. See https://github.com/kcat/openal-soft/issues/18
The problem seems to happen just on CURRENT due the clang version.

PR: 199488, 203818
Tested by: ohartman@zedat.fu-berlin.de
Approved by: mva
Approved by: ports-secteam (feld)