MFH: r513530

Fix build on GCC-based systems:

/wrkdirs/usr/ports/www/libwpe/work/libwpe-1.4.0/src/pasteboard-generic.cpp:35: error: expected nested-name-specifier before 'Pasteboard'

(If I had understood how many ports this was blocking on -quarterly,
I would have done this much earlier.)

Approved by: portmgr (tier-2 blanket)