[asan] Restore asan_device_setup compatibility with older libraries.

[eugenis]

Summary

This way new asan_device_setup, which knows about the quirks of
recent releases of Android, can be used with older ASan runtime
library (say, from an NDK release). The library is version locked to
the compiler, and is often hard or impossible to update.

compiler-rt/trunk/lib/asan/scripts/asan_device_setup

 ASAN_OPTIONS=$ASAN_OPTIONS \\
 ASAN_ACTIVATION_OPTIONS=include_if_exists=/data/local/tmp/asan.options.%b \\
 LD_PRELOAD=$_ld_preload \\
 exec $_to \$@
 
 EOF
 }
 
+# On Android-L not allowing user segv handler breaks some applications.
+# Since ~May 2017 this is the default setting; included for compatibility with
+# older library versions.
+if [[ PRE_L -eq 0 ]]; then
+    ASAN_OPTIONS="$ASAN_OPTIONS,allow_user_segv_handler=1"
+fi
+
 if [[ x$extra_options != x ]] ; then
     ASAN_OPTIONS="$ASAN_OPTIONS,$extra_options"
 fi
 
 # Zygote wrapper.
 if [[ -f "$TMPDIR/app_process64" ]]; then
   # A 64-bit device.
   if [[ ! -f "$TMPDIR/app_process64.real" ]]; then