gdb: syscalls: Update linux-defaults.xml.in

gdb: syscalls: Update linux-defaults.xml.in

Make use of the script update-linux-defaults.sh to regenerate the Linux
syscall group info against strace git commit 8c480270653d which will be
released in v6.8.

Like this:

  $ git clone https://github.com/strace/strace.git strace.git
  $ git clone https://sourceware.org/git/binutils-gdb.git gdb.git
  $ cd gdb.git/gdb/syscalls/
  $ ./update-linux-defaults.sh ~/strace.git/

Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Approved-By: John Baldwin <jhb@FreeBSD.org>