[qt5-build.eclass] Tweak qconfig.h sed expression to avoid problems.

See commit f1c2941f8b40e41e3413f4465c2edec1bb1a78a8
[dev-qt/qtcore:4] Move qconfig.h sed to qt4-build-multilib.eclass
[dev-qt/qtcore:4] Drop keepdir.

Package-Manager: portage-2.2.14