Use -Werror in external/python/cpython2

* Keep existing invalid-source-encoding and macro-redefined
  warnings to fix later.
* No -Werror for darwin_x86_64 yet. Must fix/suppress all warnings first.

Bug: 66996870
Test: build with WITH_TIDY=1
Change-Id: I7e6e1974af3ab8f763baa3b3fdbe7ae11e841844
diff --git a/Android.bp b/Android.bp
index acb1f96..8128dea 100644
--- a/Android.bp
+++ b/Android.bp
@@ -24,6 +24,8 @@
         "-Wall",
         "-Wstrict-prototypes",
         "-DPy_BUILD_CORE",
+        "-Wno-error=invalid-source-encoding",
+        "-Wno-error=macro-redefined",
         "-Wno-missing-field-initializers",
         "-Wno-shift-count-overflow",
         "-Wno-sign-compare",
@@ -37,9 +39,11 @@
         // Regenerate include dirs with android_regen.sh
         darwin_x86_64: {
             local_include_dirs: ["darwin_x86_64/pyconfig"],
+            // cflags: ["-Werror"], // still has warnings on darwin
         },
         linux_glibc_x86_64: {
             local_include_dirs: ["linux_x86_64/pyconfig"],
+            cflags: ["-Werror"],
         },
         windows: {
             enabled: false,