When configured "shared", don't build static libraries on Windows

The reason for this is that the static libraries and the DLL import
libraries are named the same on Windows.  When configured "shared",
the static libraries are unused anyway.

Reviewed-by: Rich Salz <rsalz@openssl.org>

Configurations/windows-makefile.tmpl

@@ -298,6 +298,11 @@ $objs$linklibs \$(EX_LIBS)
 EOF
  }
  sub obj2lib {
+     # Because static libs and import libs are both named the same in native
+     # Windows, we can't have both.  We skip the static lib in that case,
+     # as the shared libs are what we use anyway.
+     return "" unless $disabled{"shared"};
+
      my %args = @_;
      my $lib = $args{lib};
      my $objs = join("\n", map { $_.$objext } @{$args{objs}});