[CMake] Fix building with -DBUILD_SHARED_LIBS=ON on mingw

Set the right target name in clang/examples/Attribute.

Add a missing dependency in the TableGen GlobalISel sublibrary.

Skip building the Bye pass plugin example on windows; plugins
that should have undefined symbols that are found in the host
process aren't supported on windows - this matches what was done
for a unit test in bc8e4421.