tk+tktable: Don't pass -static-libgcc when building shared version

.. as that's clearly a dumb thing to do as it puts the same requirement on
all DLLs that are linked in. The real bug was 'fixed' by:

https://github.com/Alexpux/MINGW-packages/commit/abf850d0fe3a07eef11cbef78f727c8f58da8998

I put fixed in quotes as theres difference of opinion as to whether
some other method isn't more correct. Kai Tietz wondered if passing
-fasynchronous-unwind-tables would fix this problem, but it didn't.