WIP: Implement seccomp-bpf sandbox for nacl_helper_nonsfi.

sandbox/linux/system_headers/android_i386_ucontext.h

Index: sandbox/linux/system_headers/android_i386_ucontext.h
diff --git a/sandbox/linux/system_headers/android_i386_ucontext.h b/sandbox/linux/system_headers/android_i386_ucontext.h
index 868016b5570647413b3b864c0d2b8eece35ef039..88e2108c683b9490b2d99f180da2e0d42d294d34 100644
--- a/sandbox/linux/system_headers/android_i386_ucontext.h
+++ b/sandbox/linux/system_headers/android_i386_ucontext.h
@@ -11,7 +11,15 @@
 // except we do use sigset_t for uc_sigmask instead of a custom type.
 
 #if !defined(__BIONIC_HAVE_UCONTEXT_T)
+#if defined(__ANDORID__)
 #include <asm/sigcontext.h>
+#else
+typedef struct sigaltstack {
+  void* ss_sp;
+  int ss_flags;
+  size_t ss_size;
+} stack_t;
+#endif
 
 /* 80-bit floating-point register */
 struct _libc_fpreg {