[LLD] [MinGW] Support both "--opt value" and "--opt=value" for more options

This does the same fix as D107237 but for a couple more options,
converting all remaining cases of such options to accept both
forms, for consistency. This fixes building e.g. openldap, which
uses --image-base=<value>.

Differential Revision: https://reviews.llvm.org/D107253