Force __pnacl_pso_root to be an external declaration.

src/PNaClTranslator.cpp

Index: src/PNaClTranslator.cpp
diff --git a/src/PNaClTranslator.cpp b/src/PNaClTranslator.cpp
index 1fb84c16b76e32f44592ed8670210b7e12031439..2c9e98f1bfd5e458ee5b988eaeae655e72b33688 100644
--- a/src/PNaClTranslator.cpp
+++ b/src/PNaClTranslator.cpp
@@ -547,8 +547,8 @@ private:
   // Converts global variable declarations into constant value IDs.
   void createValueIDsForGlobalVars() {
     Ice::GlobalContext *Ctx = getTranslator().getContext();
-    for (const Ice::VariableDeclaration *Decl : *VariableDeclarations) {
-      if (!Decl->verifyLinkageCorrect(Ctx))
+    for (Ice::VariableDeclaration *Decl : *VariableDeclarations) {
+      if (!Decl->verifyLinkageCorrect(Ctx) && !Decl->forcePNaClABILinkage())
         reportLinkageError("Global", *Decl);
       Ice::Constant *C =
           getConstantSym(Decl->getName(), Decl->getSuppressMangling(),