Make DUChainReferenceCounting compile with MSVC
MSVC intentionally does not support DLL import/export of thread_local variables. The result is the following compilation error:
C:\CI\Job Build\kdevplatform\serialization\referencecounting.h(57): error C2492: 'duchainReferenceCounting': data with thread storage duration may not have dll interface
KDevelop still runs at this branch on my GNU/Linux system. KDevelop starts and completely loads two projects - kdevelop itself and WebKit - in about 60 seconds both with external and internal linkage of
This merge request is less performance-risky than the alternative !198 (closed).