cmd/internal/ld: skip dwarf output if dsymutil no-ops

Fixes #11994.

Change-Id: Icee6ffa6e3a9d15b68b4ae9b2716d65ecbdba73a
Reviewed-on: https://go-review.googlesource.com/16702Reviewed-by: Ian Lance Taylor <iant@golang.org>

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

@@ -1171,6 +1171,10 @@ func hostlink() {
 				Ctxt.Cursym = nil
 				Exitf("%s: running dsymutil failed: %v\n%s", os.Args[0], err, out)
 			}
+			// Skip combining if `dsymutil` didn't generate a file. See #11994.
+			if _, err := os.Stat(dsym); os.IsNotExist(err) {
+				return
+			}
 			// For os.Rename to work reliably, must be in same directory as outfile.
 			combinedOutput := outfile + "~"
 			if err := machoCombineDwarf(outfile, dsym, combinedOutput); err != nil {