[dev.link] cmd/link: ensure deterministic order in dynexp

dynexp is used for generating the dynamic symbol table. It is
created from a map. Sort it to ensure deterministic order.

Should fix solaris build.

Change-Id: I561b9da3a4136a7ea41139073f76c98fb069d4fa
Reviewed-on: https://go-review.googlesource.com/c/go/+/204378
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>

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

@@ -58,6 +58,7 @@ import (
 	"os/exec"
 	"path/filepath"
 	"runtime"
+	"sort"
 	"strings"
 	"sync"
 )
@@ -540,6 +541,7 @@ func setupdynexp(ctxt *Link) {
 		s := ctxt.Syms.Lookup(exp, 0)
 		dynexp = append(dynexp, s)
 	}
+	sort.Sort(byName(dynexp))
 
 	// Resolve ABI aliases in the list of cgo-exported functions.
 	// This is necessary because we load the ABI0 symbol for all

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

@@ -99,3 +99,10 @@ func contains(s []string, v string) bool {
 	}
 	return false
 }
+
+// implements sort.Interface, for sorting symbols by name.
+type byName []*sym.Symbol
+
+func (s byName) Len() int           { return len(s) }
+func (s byName) Swap(i, j int)      { s[i], s[j] = s[j], s[i] }
+func (s byName) Less(i, j int) bool { return s[i].Name < s[j].Name }