Add Rust darwin host support.

Support for building Rust modules on darwin hosts.

Bug: 140640858
Test: m libremain works on darwin
Change-Id: Ieb1ff9167de34cffbebebab31fa48da07081c8a6
diff --git a/Android.bp b/Android.bp
index b15a875b..817710e 100644
--- a/Android.bp
+++ b/Android.bp
@@ -340,6 +340,7 @@
         "rust/config/global.go",
         "rust/config/toolchain.go",
         "rust/config/whitelist.go",
+        "rust/config/x86_darwin_host.go",
         "rust/config/x86_linux_host.go",
         "rust/config/x86_64_device.go",
     ],