make the MinGW build of lupdate work for non-admin users

Windows User Access Control thinks that lupdate is an installer,
because of the string "update" in the executable name.
MSVC automatically creates and embeds a manifest into the executable
to state that lupdate doesn't need admin rights.
For MinGW we now embed a handcrafted manifest.

[ChangeLog][lupdate] Fixed lupdate requiring admin rights when built
with MinGW.

Task-number: QTBUG-36369
Change-Id: I306ba4c13014f2e39fc5785bb90bacd951726ad4
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>