cmd/link: skip TestFlagW on AIX

The internal/xcoff can only parse XCOFF with symbol table. This
test creates executables without symbol table. Skip the test.

(It might be possible to make internal/xcoff work with binaries
without symbol table? Leave it for the future.)

Fixes golang#75618.

Change-Id: I273ffefee5376d987accd5aa48c9473d2b3df055
Reviewed-on: https://go-review.googlesource.com/c/go/+/707095
Reviewed-by: David Chase <[email protected]>
Run-TryBot: Cherry Mui <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>

Author: cherrymui

src/cmd/link/dwarf_test.go

@@ -361,6 +361,9 @@ func TestDWARFLocationList(t *testing.T) {
 
 func TestFlagW(t *testing.T) {
 	testenv.MustHaveGoBuild(t)
+	if runtime.GOOS == "aix" {
+		t.Skip("internal/xcoff cannot parse file without symbol table")
+	}
 	t.Parallel()
 
 	tmpdir := t.TempDir()