Subzero. ARM32. Nonsfi.

Adds nonsfi support to the ARM32 backend.

BUG= https://bugs.chromium.org/p/nativeclient/issues/detail?id=4076
R=stichnot@chromium.org

Review URL: https://codereview.chromium.org/1665263003 .
diff --git a/runtime/szrt.c b/runtime/szrt.c
index ec6b8cd..7ac5030 100644
--- a/runtime/szrt.c
+++ b/runtime/szrt.c
@@ -63,3 +63,4 @@
 //   memset  - call @llvm.memset.p0i8.i32
 // unsandboxed_irt:
 //   __nacl_read_tp
+//   __aeabi_read_tp [arm32 only]