adbd: turn on -Wthread-safety.

not_windows doesn't include android...

Test: treehugger
Change-Id: Ie275e22c895b0c88ce9d9f677750d2bffeeebc42
diff --git a/adb/Android.bp b/adb/Android.bp
index bccc71a..91006b2 100644
--- a/adb/Android.bp
+++ b/adb/Android.bp
@@ -41,7 +41,10 @@
 
     target: {
         android: {
-            cflags: ["-DADB_HOST=0"],
+            cflags: [
+                "-DADB_HOST=0",
+                "-Wthread-safety",
+            ],
         },
 
         host: {