.pc files have extra quotes around -framework arguments in Libs: line

The .pc files installed for Qt 5.5.0 on OS X have Libs: lines like

Libs: -F${libdir} '-framework QtCore '.

This causes the Wireshark autoconf process, which uses pkg-config to find Qt, to generate Makefiles that fail to correctly link the Qt-based Wireshark, producing a pile of confusing linker errors.

(This is over and above the .pc file problems reported in QTBUG-35256, which are still unfixed as of 5.5.0.)