Binder: Split OS to Android and Unix part, abstract GetThreadId out

Bug: 302723053
Test: mma in binder folder
Test: aosp/2616196
Change-Id: I73df8fc453df0edf496960853cb0004f1c3a6a43
diff --git a/libs/binder/Android.bp b/libs/binder/Android.bp
index 6c2b313..fd2b27f 100644
--- a/libs/binder/Android.bp
+++ b/libs/binder/Android.bp
@@ -118,7 +118,8 @@
     ],
 
     srcs: [
-        "OS.cpp",
+        "OS_android.cpp",
+        "OS_unix_base.cpp",
         "RpcTransportRaw.cpp",
     ],
 
@@ -249,6 +250,7 @@
 
     srcs: [
         // Trusty-specific files
+        "OS_android.cpp",
         "trusty/logging.cpp",
         "trusty/OS.cpp",
         "trusty/RpcServerTrusty.cpp",