cmd/link: preserve symbol attributes when cloning to external

There are some symbol attributes that are encoded in the object
file. Currently, they are lost when cloning a symbol to external.
Copy them over.

Also delete CopyAttributes as it is no longer called anywhere.

Change-Id: I1497e3223a641704bf35aa3e904dd0eda2f8ec3e
Reviewed-on: https://go-review.googlesource.com/c/go/+/400574
Run-TryBot: Cherry Mui <cherryyz@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>

src/cmd/link/internal/loader/loader.go

@@ -2341,6 +2341,10 @@ func (l *Loader) cloneToExternal(symIdx Sym) {
 	// need to access the old symbol content.)
 	l.objSyms[symIdx] = objSym{l.extReader.objidx, uint32(pi)}
 	l.extReader.syms = append(l.extReader.syms, symIdx)
+
+	// Some attributes were encoded in the object file. Copy them over.
+	l.SetAttrDuplicateOK(symIdx, r.Sym(li).Dupok())
+	l.SetAttrShared(symIdx, r.Shared())
 }
 
 // Copy the payload of symbol src to dst. Both src and dst must be external
@@ -2361,31 +2365,6 @@ func (l *Loader) CopySym(src, dst Sym) {
 	// TODO: other attributes?
 }
 
-// CopyAttributes copies over all of the attributes of symbol 'src' to
-// symbol 'dst'.
-func (l *Loader) CopyAttributes(src Sym, dst Sym) {
-	l.SetAttrReachable(dst, l.AttrReachable(src))
-	l.SetAttrOnList(dst, l.AttrOnList(src))
-	l.SetAttrLocal(dst, l.AttrLocal(src))
-	l.SetAttrNotInSymbolTable(dst, l.AttrNotInSymbolTable(src))
-	if l.IsExternal(dst) {
-		l.SetAttrVisibilityHidden(dst, l.AttrVisibilityHidden(src))
-		l.SetAttrDuplicateOK(dst, l.AttrDuplicateOK(src))
-		l.SetAttrShared(dst, l.AttrShared(src))
-		l.SetAttrExternal(dst, l.AttrExternal(src))
-	} else {
-		// Some attributes are modifiable only for external symbols.
-		// In such cases, don't try to transfer over the attribute
-		// from the source even if there is a clash. This comes up
-		// when copying attributes from a dupOK ABI wrapper symbol to
-		// the real target symbol (which may not be marked dupOK).
-	}
-	l.SetAttrSpecial(dst, l.AttrSpecial(src))
-	l.SetAttrCgoExportDynamic(dst, l.AttrCgoExportDynamic(src))
-	l.SetAttrCgoExportStatic(dst, l.AttrCgoExportStatic(src))
-	l.SetAttrReadOnly(dst, l.AttrReadOnly(src))
-}
-
 // CreateExtSym creates a new external symbol with the specified name
 // without adding it to any lookup tables, returning a Sym index for it.
 func (l *Loader) CreateExtSym(name string, ver int) Sym {