Fix incorrect Rust dylib extension on darwin.

rustc expects Rust dylibs to have a .dylib extension on darwin.

Bug: 155302034
Test: rust_library_host outputs have correct extension on darwin.
Change-Id: I17b0d7eaf0f42f8186185e3f14c3a8e992c74fde
diff --git a/rust/config/x86_darwin_host.go b/rust/config/x86_darwin_host.go
index 4c16693..9dd49ff 100644
--- a/rust/config/x86_darwin_host.go
+++ b/rust/config/x86_darwin_host.go
@@ -66,6 +66,10 @@
 	return ".dylib"
 }
 
+func (t *toolchainDarwin) DylibSuffix() string {
+	return ".rustlib.dylib"
+}
+
 func (t *toolchainDarwin) ProcMacroSuffix() string {
 	return ".dylib"
 }