cmd/link: always set .dynsym info field

CL 187979 added set .dynsym info field, but it won't when
there are no global symbols. This CL sets that field
unconditionally.

Fixes #34000

Change-Id: Icc2f8bc74afdade88a377793e6760912b03686ba
Reviewed-on: https://go-review.googlesource.com/c/go/+/192600
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/link/internal/ld/elf.go

@@ -1948,10 +1948,10 @@ func Asmbelf(ctxt *Link, symo int64) {
 		for sub := s; sub != nil; sub = sub.Sub {
 			i++
 			if !sub.Attr.Local() {
-				sh.info = i
 				break
 			}
 		}
+		sh.info = i
 		shsym(sh, s)
 
 		sh = elfshname(".dynstr")