[MinGW] Don't autoexport anything from libmsvcrt or libucrtbase

These libraries contain a number of object files with compat wrappers,
in addition to the normal import library entries.

Differential Revision: https://reviews.llvm.org/D39684

llvm-svn: 317505

lld/COFF/MinGW.cpp

@@ -69,6 +69,8 @@ AutoExporter::AutoExporter() {
       "libc++",
       "libc++abi",
       "libunwind",
+      "libmsvcrt",
+      "libucrtbase",
   };
   ExcludeObjects = {
       "crt0.o",