Enable arm/linux chromium to build with gn

sandbox/linux/system_headers/arm_linux_syscalls.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Generated from the Linux kernel's calls.S.
 #ifndef SANDBOX_LINUX_SYSTEM_HEADERS_ARM_LINUX_SYSCALLS_H_
 #define SANDBOX_LINUX_SYSTEM_HEADERS_ARM_LINUX_SYSCALLS_H_
 
 #if !defined(__arm__) || !defined(__ARM_EABI__)
 #error "Including header on wrong architecture"
@@ skipping 223 matching lines @@
 #endif
 
 #if !defined(__NR_sethostname)
 #define __NR_sethostname (__NR_SYSCALL_BASE+74)
 #endif
 
 #if !defined(__NR_setrlimit)
 #define __NR_setrlimit (__NR_SYSCALL_BASE+75)
 #endif
 
+#if !defined(__NR_getrlimit)
+#define __NR_getrlimit (__NR_SYSCALL_BASE+76)

[Sam Clegg, 2015/12/02 00:42:56]

This is defined and then undefined in
debian_wheezy_arm-sysroot/usr/include/arm-linux-gnueabihf/asm/unistd.h with the
following comment:

/*                                                                              

 * The following syscalls are obsolete and no longer available for EABI.        

 */                                                                             

#if defined(__ARM_EABI__) && !defined(__KERNEL__)   
...


So is this the best solution?  Or should I use #ifdef at the use site in
mojo/runner/host/linux_sandbox.cc?

+#endif
+
 #if !defined(__NR_getrusage)
 #define __NR_getrusage (__NR_SYSCALL_BASE+77)
 #endif
 
 #if !defined(__NR_gettimeofday)
 #define __NR_gettimeofday (__NR_SYSCALL_BASE+78)
 #endif
 
 #if !defined(__NR_settimeofday)
 #define __NR_settimeofday (__NR_SYSCALL_BASE+79)
@@ skipping 1155 matching lines @@
 #if !defined(__ARM_NR_set_tls)
 #define __ARM_NR_set_tls (__ARM_NR_BASE+5)
 #endif
 
 // ARM kernel private syscall.
 #if !defined(__ARM_NR_cmpxchg)
 #define __ARM_NR_cmpxchg (__ARM_NR_BASE+0x00fff0)
 #endif
 
 #endif  // SANDBOX_LINUX_SYSTEM_HEADERS_ARM_LINUX_SYSCALLS_H_