Add qmake feature and configure option, which optimze the size of static
exectuable. Use for static build.
Enabled via configure --gc-binaries, or CONFIG += gc-binaries in 3rd party
projects.

Change-Id: I3c25b02caaef6a4afc6019afc9c67122dd11696d
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@qt.io>