Don't disable rust modules for linux_bionic

With If4300583edfb6d75bd4d984b38f73b6a406b4447, linux_bionic supports
arm64 and rust toolchain was configured to support the new target.
However, rust module types still have been disabled for linux_bionic
targets which forces many rust modules to be annotated with
target.linux_bionic_arm64.enabled: true, which will be very cumbersome.
Therefore, stop disabling the rust modules for linux_bionic.

Bug: 159685774
Test: HOST_CROSS_OS=linux_bionic m nothing
Change-Id: I68b97a43e8252fb82da6e87b3481fa237e1f2691

rust/compiler.go

@@ -216,8 +216,8 @@ func (compiler *baseCompiler) compilerDeps(ctx DepsContext, deps Deps) Deps {
 
 	if !Bool(compiler.Properties.No_stdlibs) {
 		for _, stdlib := range config.Stdlibs {
-			// If we're building for the primary host target, use the compiler's stdlibs
-			if ctx.Host() && ctx.TargetPrimary() {
+			// If we're building for the primary arch of the build host, use the compiler's stdlibs
+			if ctx.Target().Os == android.BuildOs && ctx.TargetPrimary() {
 				stdlib = stdlib + "_" + ctx.toolchain().RustTriple()
 			}