Recognize newer libmng versions in config test

libmng 2.0.x has been released and is compatible and usable, but since
it no longer provides a VERSION_MAJOR macro, the config test would fail.

Task-number: QTBUG-34894
Change-Id: I36f6ed9d69dbae88feb1b88ce099bf36c9283133
Reviewed-by: Liang Qi <liang.qi@digia.com>
(cherry picked from qtimageformats/9ae386653c321c8ddc10fad5ea88f32ebb3d3ffe)
Keep the copied files as writable

Mac's strip tool doesn't work if the file is read-only. Some of the
libraries we copy might be read-only (like those installed by
HomeBrew) and that would cause stripping to fail.

(cherry-picked from qttools commit f82499e6508975188b38cb396280c901e4274cd7)
Change-Id: Ie8caa853a26794ec97ec84354d9f7bb142cce993
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@digia.com>