Replace __unused in kernel headers with __linux_unused to avoid
conflicts with __unused macro in sys/cdefs.h

Change-Id: Ice664397e0b7c7a90795012f30be5e43a9675525
diff --git a/libc/kernel/arch-arm/asm/ucontext.h b/libc/kernel/arch-arm/asm/ucontext.h
index 769f694..f54a7f1 100644
--- a/libc/kernel/arch-arm/asm/ucontext.h
+++ b/libc/kernel/arch-arm/asm/ucontext.h
@@ -27,7 +27,7 @@
  struct sigcontext uc_mcontext;
 /* WARNING: DO NOT EDIT, AUTO-GENERATED CODE - SEE TOP FOR INSTRUCTIONS */
  sigset_t uc_sigmask;
- int __unused[32 - (sizeof (sigset_t) / sizeof (int))];
+ int __linux_unused[32 - (sizeof (sigset_t) / sizeof (int))];
  unsigned long uc_regspace[128] __attribute__((__aligned__(8)));
 };
 /* WARNING: DO NOT EDIT, AUTO-GENERATED CODE - SEE TOP FOR INSTRUCTIONS */