mk: rt.mk regression patch for mingw32 after #6176
mk: target.mk host.mk fix for duplicated rules of mingw32 after #6235
auto merge of #6295 : yichoi/rust/pull-mingw32, r=brson

fix for #6279 #6253

mk: rt.mk regression patch for mingw32 after #6176

currently do not pass optimization option just make it works only

mk: target.mk host.mk fix for duplicated rules of mingw32 after #6235

It can be simply fixed with CFG_LIB check whether bin or lib however considering multiple target triples with linux and windows, CFG_LIB needs to configurable #5223 and #5577