GenericGCC: do not link shared objects transitively

This is consistent with the libraryPaths property and MSVC.

Change-Id: I3bc9a17640e89d61764abb8fa5736f1b47d1663f
Reviewed-by: Christian Kandeler <christian.kandeler@digia.com>
Make Info.plist composition more robust.

Building will no longer fail if the platform, SDK, or toolchains'
respective plist files do not exist, or if an SDK path is not specified.

Task-number: QBS-348
Change-Id: Ie66194c09700a38b1c0ce39c4641af27580aefd6
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>
Make Loader more reusable.

JavaScript exceptions left over from previous runs could interfere
with evaluation, so clean those up first.

Change-Id: Id7908a1bdc3b1709fa494c13d833cf993799f566
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>