base: export GetThreadId.

and stop using the incorrect (on Mac) version in adb..

Test: mma
Change-Id: If28f6c8d73b03db863be13ed88df81422c3aef87
diff --git a/base/Android.bp b/base/Android.bp
index 5d70d47..7b0ba11 100644
--- a/base/Android.bp
+++ b/base/Android.bp
@@ -50,6 +50,7 @@
         "quick_exit.cpp",
         "stringprintf.cpp",
         "strings.cpp",
+        "threads.cpp",
         "test_utils.cpp",
     ],