Introducing external weak linkage. Darwin codegen should be added later.

llvm-svn: 32052
diff --git a/llvm/lib/Target/X86/X86ATTAsmPrinter.cpp b/llvm/lib/Target/X86/X86ATTAsmPrinter.cpp
index 7784f62..88d0c7c 100755
--- a/llvm/lib/Target/X86/X86ATTAsmPrinter.cpp
+++ b/llvm/lib/Target/X86/X86ATTAsmPrinter.cpp
@@ -255,6 +255,10 @@
       }       
       O << Name;
     }
+
+    if (GV->hasExternalWeakLinkage()) {
+      ExtWeakSymbols.insert(Name);
+    }
     
     int Offset = MO.getOffset();
     if (Offset > 0)