[msan] Change linkage type of __msan_track_origins.

LinkOnceODRLinkage globals may be removed in GlobalOpt if not used in the
current module.

llvm-svn: 169377
diff --git a/llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp b/llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp
index 81cbb07..4680994 100644
--- a/llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp
+++ b/llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp
@@ -244,7 +244,7 @@
   appendToGlobalCtors(M, cast<Function>(M.getOrInsertFunction(
                       "__msan_init", IRB.getVoidTy(), NULL)), 0);
 
-  new GlobalVariable(M, IRB.getInt32Ty(), true, GlobalValue::LinkOnceODRLinkage,
+  new GlobalVariable(M, IRB.getInt32Ty(), true, GlobalValue::WeakODRLinkage,
                      IRB.getInt32(ClTrackOrigins), "__msan_track_origins");
 
   // Create the callback.