Internalize gpr_thd except for id and currentid
diff --git a/BUILD b/BUILD
index 561993a..1c03b7d 100644
--- a/BUILD
+++ b/BUILD
@@ -76,7 +76,7 @@
     "include/grpc/support/sync_generic.h",
     "include/grpc/support/sync_posix.h",
     "include/grpc/support/sync_windows.h",
-    "include/grpc/support/thd.h",
+    "include/grpc/support/thd_id.h",
     "include/grpc/support/time.h",
 ]
 
@@ -494,7 +494,7 @@
         "src/core/lib/gpr/spinlock.h",
         "src/core/lib/gpr/string.h",
         "src/core/lib/gpr/string_windows.h",
-        "src/core/lib/gpr/thd_internal.h",
+        "src/core/lib/gpr/thd.h",
         "src/core/lib/gpr/time_precise.h",
         "src/core/lib/gpr/tls.h",
         "src/core/lib/gpr/tls_gcc.h",