Do not set entry-point for Windows

Bug: http://b/62424007

This breaks 64-bit Windows executables.  Probably due to the Clang
migration, the entry-point need not be set even for 32-bit executables.

Test: 32-bit and 64-bit aapt2_tests.exe and ziparchive-tests.exe can
start.  (There are some failed tests, though).

Change-Id: Id3a7d3d2802f6b671332afff4558840bdabddeb5

cc/binary.go

@@ -216,9 +216,6 @@ func (binary *binaryDecorator) linkerFlags(ctx ModuleContext, flags Flags) Flags
 	if ctx.Host() && !binary.static() {
 		if !ctx.Config().IsEnvTrue("DISABLE_HOST_PIE") {
 			flags.LdFlags = append(flags.LdFlags, "-pie")
-			if ctx.Windows() {
-				flags.LdFlags = append(flags.LdFlags, "-Wl,-e_mainCRTStartup")
-			}
 		}
 	}