[SystemZ] Extend RISBG optimization

The handling of ANY_EXTEND and ZERO_EXTEND was too strict.  In this context
we can treat ZERO_EXTEND in much the same way as an AND and then also handle
outermost ZERO_EXTENDs.

I couldn't find a test that benefited from the ANY_EXTEND change, but it's
more obvious to write it this way once SIGN_EXTEND and ZERO_EXTEND are
handled differently.
[PECOFF] Create noname or data symbols as such.

If a symbol in an import library is marked as "data", the linker will not
create a jump table entry for the symbol, since jump table makes sense only
for a symbol pointing to a function.

I don't think NONAME attribute has a meaning when creating an import library.
The attribute is emitted for debugging purpose.