Define Symbol::copyBody function.

This patch adds a utility function to Symbol. This function should
be useful in https://reviews.llvm.org/D33680 too.

llvm-svn: 306587
diff --git a/lld/ELF/Symbols.h b/lld/ELF/Symbols.h
index 406fd8e..8fcdc21 100644
--- a/lld/ELF/Symbols.h
+++ b/lld/ELF/Symbols.h
@@ -379,6 +379,8 @@
 
   SymbolBody *body() { return reinterpret_cast<SymbolBody *>(Body.buffer); }
   const SymbolBody *body() const { return const_cast<Symbol *>(this)->body(); }
+
+  void copyBody(Symbol *Other);
 };
 
 void printTraceSymbol(Symbol *Sym);