How to get shared library extension in .pro

[Gourmet]

I need automatically get shared library extension being created by project. Project creates shared library which extension is different in different OSes. On top of project I have TEMPLATE = lib line. How can I get system-depended extension for QMAKE_POST_LINK command? Not ${TARGET_EXT} nor ${QMAKE_EXTENSION_SHLIB} works. In both cases extension appears empty.