Use -Werror in external/minijail

Bug: 66996870
Test: build with WITH_TIDY=1
Change-Id: I31daf27a7bc1ad3912ecee0a62eced0025a64495
diff --git a/Android.bp b/Android.bp
index a90d654..03b0530 100644
--- a/Android.bp
+++ b/Android.bp
@@ -53,6 +53,8 @@
     cflags: [
         "-dD",
         "-E",
+        "-Wall",
+        "-Werror",
     ],
 }
 
@@ -72,6 +74,8 @@
     cflags: [
         "-dD",
         "-E",
+        "-Wall",
+        "-Werror",
     ],
 }