Configure the default arch variant features per-OS

The minimum set of supported features are different between Android and
Linux with X86_64. So while the list of variants and features are still
technically correct, and may be shared more in the future, the default
needs to be configured differently.

Bug: 120208462
Test: add `host_supported: true` to libopus; m libopus
Change-Id: Ib79707d17b852f77341026085230c026b6386b78

cc/config/x86_64_device.go

@@ -81,7 +81,7 @@ func init() {
 		"aes_ni",
 		"avx",
 		"popcnt")
-	android.RegisterArchVariantFeatures(android.X86_64, "",
+	android.RegisterDefaultArchVariantFeatures(android.Android, android.X86_64,
 		"ssse3",
 		"sse4",
 		"sse4_1",