message: util: Make sure syscall numbers used in profile are defined
  Define the following syscall numbers for x86_64, so that the profile
  will be the same no matter what kernel is built against, including
  kernels that don't have `__NR_statx`:
  ```c++
  #define __NR_statx 332
  #define __NR_getrandom 318
  #define __NR_membarrier 324
  ```
diff: @@ -44,6 +44,20 @@ bool g_syscall_sandbox_log_violation_before_terminating{false};
  #define SECCOMP_RET_KILL_PROCESS 0x80000000U
  #endif
  +// Define system call numbers for x86_64 that are referenced in the system call profile
  +// but not provided by the kernel headers used in the GUIX build.
  +#ifndef __NR_statx
  +#define __NR_statx 332
  +#endif
  +
  +#ifndef __NR_getrandom
  +#define __NR_getrandom 318
  +#endif
  +
  +#ifndef __NR_membarrier
  +#define __NR_membarrier 324
  +#endif
  +
  // This list of syscalls in LINUX_SYSCALLS is only used to map syscall numbers to syscall names in
  // order to be able to print user friendly error messages which include the syscall name in addition
  // to the syscall number.
  @@ -162,9 +176,7 @@ const std::map<uint32_t, std::string> LINUX_SYSCALLS{
  {__NR_getpmsg, "getpmsg"},
  {__NR_getppid, "getppid"},
  {__NR_getpriority, "getpriority"},
  -#if defined(__NR_getrandom)
  {__NR_getrandom, "getrandom"},
  -#endif // defined(__NR_getrandom)
  {__NR_getresgid, "getresgid"},
  {__NR_getresuid, "getresuid"},
  {__NR_getrlimit, "getrlimit"},
  @@ -212,9 +224,7 @@ const std::map<uint32_t, std::string> LINUX_SYSCALLS{
  {__NR_lstat, "lstat"},
  {__NR_madvise, "madvise"},
  {__NR_mbind, "mbind"},
  -#if defined(__NR_membarrier)
  {__NR_membarrier, "membarrier"},
  -#endif // defined(__NR_membarrier)
  {__NR_memfd_create, "memfd_create"},
  {__NR_migrate_pages, "migrate_pages"},
  {__NR_mincore, "mincore"},
  @@ -515,9 +525,7 @@ public:
  {
  allowed_syscalls.insert(__NR_brk); // change data segment size
  allowed_syscalls.insert(__NR_madvise); // give advice about use of memory
  -#if defined(__NR_membarrier)
  allowed_syscalls.insert(__NR_membarrier); // issue memory barriers on a set of threads
  -#endif // defined(__NR_membarrier)
  allowed_syscalls.insert(__NR_mlock); // lock memory
  allowed_syscalls.insert(__NR_mmap); // map files or devices into memory
  allowed_syscalls.insert(__NR_mprotect); // set protection on a region of memory
  @@ -597,9 +605,7 @@ public:
  void AllowGetRandom()
  {
  -#if defined(__NR_getrandom)
  allowed_syscalls.insert(__NR_getrandom); // obtain a series of random bytes
  -#endif // defined(__NR_getrandom)
  }
  void AllowGetSimpleId()
  