Ensure that Qt public headers compile with strict flags

Ensure that Qt public headers compile with strict flags

Those from
http://wiki.qt-project.org/Coding_Conventions#Conventions_for_public_header_files
(unfortunatey -Wold-style-cast cannot be used due to the glibc macro bswap_16)
and many Qt defines that disable casts.

Change-Id: I97ac707a101df9819e8c031fa75a31b30e20247f
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>