fixups for extern and pragma

Summary:
add "Objective-C" linkage type

fix extern(C++) and add support for extern(C++, ...)

fix pragma(foo, ...)

add more well-known pragma types

Reviewers: dhaumann

Reviewed By: dhaumann

Subscribers: dhaumann, kwrite-devel, kde-frameworks-devel

Tags: Kate, Frameworks

Differential Revision: https://phabricator.kde.org/D17460