[MinGW] Ignore the --plugin and --plugin-opt option

GCC can use LLD with -fuse-ld=lld for MinGW these days, but by
default these options are passed to the linker (unless -fno-lto
is passed to the GCC driver).

Differential Revision: https://reviews.llvm.org/D57304

llvm-svn: 352459

lld/MinGW/Options.td

@@ -78,3 +78,9 @@ def version: F<"version">, HelpText<"Display the version number and exit">;
 def alias_entry_e: JoinedOrSeparate<["-"], "e">, Alias<entry>;
 def alias_strip_s: Flag<["-"], "s">, Alias<strip_all>;
 def alias_strip_S: Flag<["-"], "S">, Alias<strip_debug>;
+
+// Ignored options
+def: S<"plugin">;
+def: J<"plugin=">;
+def: S<"plugin-opt">;
+def: J<"plugin-opt=">;