[LLD] [MinGW] Handle the --dll option (#68575)

Treat this as an alias for the --shared option.

In practice in GNU ld, they aren't exact aliases but there are small
subtle differences in what happens and what doesn't, when they are set,
but those differences are probably not intended by users who might be
using the --dll option (which gets passed by -mdll in the compiler
driver), and the differences are within the area where small details
differ between LLD and GNU ld anyway.