MediaTranscodingService: Add some missing build flags to Android.bp

The build flag uncover some locking are missed and this CL also fixes
them.

Bug: 145233472
Test: Unit test
Change-Id: Ide999b95f064adf14967cc2e36331524e83426d2
diff --git a/media/libmediatranscoding/Android.bp b/media/libmediatranscoding/Android.bp
index e3e87e1..2a6601a 100644
--- a/media/libmediatranscoding/Android.bp
+++ b/media/libmediatranscoding/Android.bp
@@ -55,9 +55,13 @@
     ],
 
     cflags: [
-        "-Werror",
-        "-Wno-error=deprecated-declarations",
         "-Wall",
+        "-Werror",
+        "-Wformat",
+        "-Wno-error=deprecated-declarations",
+        "-Wthread-safety",
+        "-Wunused",
+        "-Wunreachable-code",
     ],
 
     sanitize: {