Turn off BTI in python

Python depends on libffi, which has BTI disabled.  Disable it here
too to avoid link errors.

Test: builds
Change-Id: I31004c273df113502548c576bccc482a8ed5eaec

Android.bp

diff --git a/Android.bp b/Android.bp
index 29c1355..1bfdb5a 100644
--- a/Android.bp
+++ b/Android.bp
@@ -97,6 +97,8 @@
 cpython3_cc_defaults {
     name: "py3-interp-defaults",
     defaults_visibility: ["//visibility:private"],
+    // Dependency libffi has bti turned off, which requires turning it off here.
+    defaults: ["no_bti"],
     cflags: [
         "-fwrapv",
         "-O3",