cmd/link: set Fieldtrack symbol type to SDATA

Fixes #20316

Change-Id: I2553ad9a82dfcb30f020c2a3e37b868111425a20
Reviewed-on: https://go-review.googlesource.com/43151
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

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

@@ -360,6 +360,7 @@ func fieldtrack(ctxt *Link) {
 		return
 	}
 	addstrdata(ctxt, *flagFieldTrack, buf.String())
+	s.Type = SDATA
 }
 
 func (ctxt *Link) addexport() {