Use -Werror in external/cblas

Bug: 66996870
Test: build with WITH_TIDY=1
Change-Id: I09f56274cf61955c21dd8fed1999ad7cbbe29221
diff --git a/Android.bp b/Android.bp
index 4e439d1..c4a0de5 100644
--- a/Android.bp
+++ b/Android.bp
@@ -162,6 +162,7 @@
         "src/xerbla.c",
     ],
 
+    cflags: ["-Werror"],
     export_include_dirs: ["include"],
 }