cmd/link/internal/ld: modify -pagezero_size to please iTunes Connect validation for iOS.

This change modifies go to create iOS arm64 binaries that pass iTunes
upload validation. Tested with xcode 9.0.1 macOS 10.13.

Fixes #22402.

Change-Id: I3f14c6ac85065e2da88d06edc8682947f6f1cd47
Reviewed-on: https://go-review.googlesource.com/72730Reviewed-by: David Crawshaw <crawshaw@golang.org>

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

@@ -1105,7 +1105,10 @@ func (ctxt *Link) hostlink() {
 	switch ctxt.BuildMode {
 	case BuildModeExe:
 		if ctxt.HeadType == objabi.Hdarwin {
-			argv = append(argv, "-Wl,-pagezero_size,4000000")
+			// __PAGEZERO segment size determined empirically.
+			// XCode 9.0.1 successfully uploads an iOS app with this value.
+			// Also works for macOS apps.
+			argv = append(argv, "-Wl,-pagezero_size,100000000")
 		}
 	case BuildModePIE:
 		// ELF.