Fix to compile successfully with -Wundef

lss/linux_syscall_support.h

 /* Copyright (c) 2005-2011, Google Inc.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 1328 matching lines @@
 #define __NR_move_pages         301
 #endif
 #ifndef __NR_getcpu
 #define __NR_getcpu             302
 #endif
 /* End of powerpc defininitions                                              */
 #endif
 
 
 /* After forking, we must make sure to only call system calls.               */
-#if __BOUNDED_POINTERS__
+#if defined(__BOUNDED_POINTERS__)
   #error "Need to port invocations of syscalls for bounded ptrs"
 #else
   /* The core dumper and the thread lister get executed after threads
    * have been suspended. As a consequence, we cannot call any functions
    * that acquire locks. Unfortunately, libc wraps most system calls
    * (e.g. in order to implement pthread_atfork, and to make calls
    * cancellable), which means we cannot call these functions. Instead,
    * we have to call syscall() directly.
    */
   #undef LSS_ERRNO
@@ skipping 12 matching lines @@
   #else
     #define LSS_INLINE static inline
   #endif
 
   /* Allow the including file to override the prefix used for all new
    * system calls. By default, it will be set to "sys_".
    */
   #undef LSS_NAME
   #ifndef SYS_PREFIX
     #define LSS_NAME(name) sys_##name
-  #elif SYS_PREFIX < 0
+  #elif defined(SYS_PREFIX) && SYS_PREFIX < 0
     #define LSS_NAME(name) name
-  #elif SYS_PREFIX == 0
+  #elif defined(SYS_PREFIX) && SYS_PREFIX == 0
     #define LSS_NAME(name) sys0_##name
-  #elif SYS_PREFIX == 1
+  #elif defined(SYS_PREFIX) && SYS_PREFIX == 1
     #define LSS_NAME(name) sys1_##name
-  #elif SYS_PREFIX == 2
+  #elif defined(SYS_PREFIX) && SYS_PREFIX == 2
     #define LSS_NAME(name) sys2_##name
-  #elif SYS_PREFIX == 3
+  #elif defined(SYS_PREFIX) && SYS_PREFIX == 3
     #define LSS_NAME(name) sys3_##name
-  #elif SYS_PREFIX == 4
+  #elif defined(SYS_PREFIX) && SYS_PREFIX == 4
     #define LSS_NAME(name) sys4_##name
-  #elif SYS_PREFIX == 5
+  #elif defined(SYS_PREFIX) && SYS_PREFIX == 5
     #define LSS_NAME(name) sys5_##name
-  #elif SYS_PREFIX == 6
+  #elif defined(SYS_PREFIX) && SYS_PREFIX == 6
     #define LSS_NAME(name) sys6_##name
-  #elif SYS_PREFIX == 7
+  #elif defined(SYS_PREFIX) && SYS_PREFIX == 7
     #define LSS_NAME(name) sys7_##name
-  #elif SYS_PREFIX == 8
+  #elif defined(SYS_PREFIX) && SYS_PREFIX == 8
     #define LSS_NAME(name) sys8_##name
-  #elif SYS_PREFIX == 9
+  #elif defined(SYS_PREFIX) && SYS_PREFIX == 9
     #define LSS_NAME(name) sys9_##name
   #endif
 
   #undef  LSS_RETURN
   #if (defined(__i386__) || defined(__x86_64__) || defined(__ARM_ARCH_3__) \
        || defined(__ARM_EABI__))
   /* Failing system calls return a negative result in the range of
    * -1..-4095. These are "errno" values with the sign inverted.
    */
   #define LSS_RETURN(type, res)                                               \
@@ skipping 2100 matching lines @@
     }
   #endif
 #endif
 
 #if defined(__cplusplus) && !defined(SYS_CPLUSPLUS)
 }
 #endif
 
 #endif
 #endif