cmd/link: use gold when dynamic linking on arm,arm64 only on Linux and Android

Fixes freebsd/arm build.

Change-Id: Id9b1905a5335f86d317dab7514e0ce7cb74aba1d
Reviewed-on: https://go-review.googlesource.com/c/go/+/193537
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

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

@@ -1262,7 +1262,7 @@ func (ctxt *Link) hostlink() {
 		// from the beginning of the section (like sym.STYPE).
 		argv = append(argv, "-Wl,-znocopyreloc")
 
-		if ctxt.Arch.InFamily(sys.ARM, sys.ARM64) {
+		if ctxt.Arch.InFamily(sys.ARM, sys.ARM64) && (objabi.GOOS == "linux" || objabi.GOOS == "android") {
 			// On ARM, the GNU linker will generate COPY relocations
 			// even with -znocopyreloc set.
 			// https://sourceware.org/bugzilla/show_bug.cgi?id=19962