Introducing the "linker_weak" linkage type. This will be used for Objective-C

metadata types which should be marked as "weak", but which the linker will
remove upon final linkage. For example, the "objc_msgSend_fixup_alloc" symbol is
defined like this:

       .globl l_objc_msgSend_fixup_alloc
       .weak_definition l_objc_msgSend_fixup_alloc
       .section __DATA, __objc_msgrefs, coalesced
       .align 3
l_objc_msgSend_fixup_alloc:
        .quad   _objc_msgSend_fixup
        .quad   L_OBJC_METH_VAR_NAME_1

This is different from the "linker_private" linkage type, because it can't have
the metadata defined with ".weak_definition".

llvm-svn: 107205

llvm/lib/Bitcode/Writer/BitcodeWriter.cpp

@@ -313,6 +313,7 @@ static unsigned getEncodedLinkage(const GlobalValue *GV) {
   case GlobalValue::LinkOnceODRLinkage:         return 11;
   case GlobalValue::AvailableExternallyLinkage: return 12;
   case GlobalValue::LinkerPrivateLinkage:       return 13;
+  case GlobalValue::LinkerWeakLinkage:          return 14;
   }
 }