[MinGW] [ARM] Add stubs for potential automatic dllimported variables

The runtime pseudo relocations can't handle the ARM format embedded
addresses in movw/movt pairs. By using stubs, the potentially
dllimported addresses can be touched up by the runtime pseudo relocation
framework.

Differential Revision: https://reviews.llvm.org/D51450

llvm-svn: 341176
diff --git a/llvm/lib/Target/ARM/ARMBaseInstrInfo.cpp b/llvm/lib/Target/ARM/ARMBaseInstrInfo.cpp
index 1b626ff..9a4614c 100644
--- a/llvm/lib/Target/ARM/ARMBaseInstrInfo.cpp
+++ b/llvm/lib/Target/ARM/ARMBaseInstrInfo.cpp
@@ -5081,6 +5081,7 @@
   using namespace ARMII;
 
   static const std::pair<unsigned, const char *> TargetFlags[] = {
+      {MO_COFFSTUB, "arm-coffstub"},
       {MO_GOT, "arm-got"},
       {MO_SBREL, "arm-sbrel"},
       {MO_DLLIMPORT, "arm-dllimport"},