Generated .pc files contain wrong prefix when crosscompiling

The generated .pc files contain .../sysroot/usr as prefix, but packages usually only have /usr even when crosscompiling:

root@devpool21:/tmp/e2/build# pkg-config --variable prefix Qt5Nfc                                                                                                  
/opt/emlix/test/sysroot/usr 
root@devpool21:/tmp/e2/build# pkg-config --variable prefix freetype2 
/usr

The other paths in the file usually refer to ${prefix}, but are always hardcoded. This may make sense for unusual configurations, but I would feel safer if they would refer to prefix when they are inside that directory.

This is probably also wrong in 5.9.