[gdb/record] Support recording syscall accept4

While reviewing the enum gdb_syscall entries with values >= 500, I noticed
that gdb_sys_accept exists, but gdb_sys_accept4 doesn't, while recording
support is essentially the same, given that the difference in interface is
only an extra int parameter:
...
int accept (int sockfd, struct sockaddr *addr, socklen_t *addrlen);
int accept4 (int sockfd, struct sockaddr *addr, socklen_t *addrlen, int flags);
...

Fix this by:
- adding gdb_sys_accept4,
- supporting it in record_linux_system_call alongside gdb_sys_accept, and
- mapping to gdb_sys_accept4 in various syscall canonicalization functions.

The usual thing to do before the rewrite of i386_canonicalize_syscall would
have been to use the value from arch/x86/entry/syscalls/syscall_32.tbl:
...
  gdb_sys_accept4 = 364,
...
but that's no longer necessary, so instead we use some >= 500 value:
...
  gdb_sys_accept4 = 533,
...
to steer clear of the space where ppc_canonicalize_syscall and
s390_canonicalize_syscall do hard-coded number magic.

Tested on x86_64-linux, with and without target board unix/-m32, and
aarch64-linux.

Approved-By: Guinevere Larsen <guinevere@redhat.com>

gdb/amd64-linux-tdep.h

@@ -302,6 +302,7 @@ enum amd64_syscall {
   amd64_sys_sync_file_range = 277,
   amd64_sys_vmsplice = 278,
   amd64_sys_move_pages = 279,
+  amd64_sys_accept4 = 288,
   amd64_sys_pipe2 = 293,
   amd64_sys_getrandom = 318
 };
@@ -553,6 +554,7 @@ enum amd64_x32_syscall {
   amd64_x32_sys_splice = (amd64_x32_syscall_bit + 275),
   amd64_x32_sys_tee = (amd64_x32_syscall_bit + 276),
   amd64_x32_sys_sync_file_range = (amd64_x32_syscall_bit + 277),
+  amd64_x32_sys_accept4 = (amd64_x32_syscall_bit + 288),
   amd64_x32_sys_rt_sigaction = (amd64_x32_syscall_bit + 512),
   amd64_x32_sys_rt_sigreturn = (amd64_x32_syscall_bit + 513),
   amd64_x32_sys_ioctl = (amd64_x32_syscall_bit + 514),