make __func__ a special static local

The __func__ static local variable should be deemed "special", because
it doesn't need to be correlated and should be included when needed by
an include function.

I don't have a test case for F20, but this fixes the following types of
issues when doing a full-tree recompile on RHEL 7:

    ERROR: cifssmb.o: object size mismatch: __func__.49322
    ERROR: btmrvl_main.o: kpatch_correlate_static_local_variables: 982: static local variable __func__.44657 not used
    ERROR: iwch_qp.o: .rodata.__func__.46024 section header details differ