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

android/config.go

@@ -303,7 +303,7 @@ func NewConfig(srcDir, buildDir string) (Config, error) {
 	}
 
 	if archConfig != nil {
-		androidTargets, err := decodeArchSettings(archConfig)
+		androidTargets, err := decodeArchSettings(Android, archConfig)
 		if err != nil {
 			return Config{}, err
 		}