Implement decoding of io_uring_* syscalls

Implement decoding of io_uring_* syscalls

... introduced by Linux kernel commits v5.1-rc1~99^2~14,
v5.1-rc1~99^2~7, and v5.1-rc7~24^2.

* configure.ac (AC_CHECK_HEADERS): Add linux/io_uring.h.
* io_uring.c: New file.
* Makefile.am (strace_SOURCES): Add it.
* pathtrace.c (pathtrace_match_set): Add SEN_io_uring_enter,
SEN_io_uring_register, and SEN_io_uring_setup.
* xlat/uring_enter_flags.in: New file.
* xlat/uring_register_opcodes.in: Likewise.
* linux/32/syscallent.h [425, 426, 427]: Wire up io_uring_setup,
io_uring_enter, and io_uring_register.
* linux/64/syscallent.h: Likewise.
* linux/arm/syscallent.h: Likewise.
* linux/hppa/syscallent.h: Likewise.
* linux/i386/syscallent.h: Likewise.
* linux/m68k/syscallent.h: Likewise.
* linux/microblaze/syscallent.h: Likewise.
* linux/powerpc/syscallent.h: Likewise.
* linux/powerpc64/syscallent.h: Likewise.
* linux/s390/syscallent.h: Likewise.
* linux/s390x/syscallent.h: Likewise.
* linux/sh/syscallent.h: Likewise.
* linux/sh64/syscallent.h: Likewise.
* linux/sparc/syscallent.h: Likewise.
* linux/sparc64/syscallent.h: Likewise.
* linux/x32/syscallent.h: Likewise.
* linux/x86_64/syscallent.h: Likewise.
* linux/xtensa/syscallent.h: Likewise.
* linux/alpha/syscallent.h [535, 536, 537]: Likewise.
* linux/ia64/syscallent.h [1024 + 425, 1024 + 426, 1024 + 427]: Likewise.
* linux/mips/syscallent-n32.h [6425, 6426, 6427]: Likewise.
* linux/mips/syscallent-n64.h [5425, 5426, 5427]: Likewise.
* linux/mips/syscallent-o32.h [4425, 4426, 4427]: Likewise.
* NEWS: Mention this change.
* tests/io_uring_enter.c: New file.
* tests/io_uring_register.c: Likewise.
* tests/io_uring_setup.c: Likewise.
* tests/gen_tests.in (io_uring_enter, io_uring_register,
io_uring_setup): New entries.
* tests/pure_executables.list: Add io_uring_enter, io_uring_register,
and io_uring_setup.
* tests/.gitignore: Likewise.