fix some compiler warnings

fix some compiler warnings

the list of upstream commits is incomplete, the Qt(5) devs have taken care
of many warnings and I have not scoped trough all of the repos and commits
to find them out and list them. I've made some changes on my own too

upstream commits:
https://github.com/qtproject/qtsvg/commit/fece2474fe7915db73c7cc4cc115cdac2f636377
https://github.com/qtproject/qtbase/commit/e6799c6e336ef1e79ce4ade33db336f67b7f588b
https://github.com/qtproject/qtbase/commit/64a7ac344ee324d47b96b411482b666cc619633f

Signed-off-by: Ivailo Monev <xakepa10@gmail.com>