Jansa/sstate fixes

qtdeclarative and deps now builds without any known issues with sstate, without unsafe flags for cross-compilation like -L/usr/lib in .prl files etc.

Tested on qemuarm, waiting for qemux86 build to confirm.

Fixed issues are described in commits and overview is here:
https://github.com/meta-qt5/meta-qt5/wiki/Building-with-OE