DBus1 (1.12) configuration file breaks PKG_CONFIG environment
variables and will thus prevent other libraries to be picked up
by pkgconfig. Main sympthom is that xproto is not getting picked
up anymore, which results in hundreds of lines of warnings about
this being printed.
Work around that by wrapping the call to find_package(DBus1) and
restoring the environment.
Change-Id: Ia69f10b014dddc32045b40972500a843e5d29b38
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>
400f94109d