Add compiler:c11 to USES to fix build on GCC-based systems:
/wrkdirs/usr/ports/audio/noise-suppression-for-voice-lv2/work/noise-suppression-for-voice-0.91-1-ge391a9b/src/lv2_plugin/lv2core/Plugin.hpp:205: error: expected identifier before '...' token
Approved by: portmgr (tier-2 blanket)