Use -Werror in external/jemalloc

Bug: 66996870
Test: build with WITH_TIDY=1
Change-Id: If4cfcdd6fb08b6c5cbe6e38df478b9265e045628
diff --git a/Android.bp b/Android.bp
index f59a653..0dd1e94 100644
--- a/Android.bp
+++ b/Android.bp
@@ -19,6 +19,7 @@
     "-O3",
     "-funroll-loops",
     "-fvisibility=hidden",
+    "-Werror",
     "-Wno-unused-parameter",
     "-Wno-type-limits",
 ]