When a host system has kernel headers that are newer than a compiling
kernel, mksyscalltbl fails with errors such as:

  <stdin>: In function 'main':
  <stdin>:271:44: error: '__NR_kexec_file_load' undeclared (first use in this function)
  <stdin>:271:44: note: each undeclared identifier is reported only once for each function it appears in
  <stdin>:272:46: error: '__NR_pidfd_send_signal' undeclared (first use in this function)
  <stdin>:273:43: error: '__NR_io_uring_setup' undeclared (first use in this function)
  <stdin>:274:43: error: '__NR_io_uring_enter' undeclared (first use in this function)
  <stdin>:275:46: error: '__NR_io_uring_register' undeclared (first use in this function)
  tools/perf/arch/arm64/entry/syscalls//mksyscalltbl: line 48: /tmp/create-table-xvUQdD: Permission denied

mksyscalltbl is compiled with default host includes, but run with
compiling kernel tree includes, causing some syscall numbers to being
undeclared.

Committer testing:

Before this patch, in my cross build environment, no build problems, but
these new syscalls were not in the syscalls.c generated from the
unistd.h file, which is a bug, this patch fixes it:

perfbuilder@6e20056ed532:/git/perf$ tail /tmp/build/perf/arch/arm64/include/generated/asm/syscalls.c
	[292] = "io_pgetevents",
	[293] = "rseq",
	[294] = "kexec_file_load",
	[424] = "pidfd_send_signal",
	[425] = "io_uring_setup",
	[426] = "io_uring_enter",
	[427] = "io_uring_register",
	[428] = "syscalls",
};
perfbuilder@6e20056ed532:/git/perf$ strings /tmp/build/perf/perf | egrep '^(io_uring_|pidfd_|kexec_file)'
kexec_file_load
pidfd_send_signal
io_uring_setup
io_uring_enter
io_uring_register
perfbuilder@6e20056ed532:/git/perf$
$

Well, there is that last "syscalls" thing, but that looks like some
other bug.
Signed-off-by: Vitaly Chikunov <vt@altlinux.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Tested-by: Michael Petlan <mpetlan@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Hendrik Brueckner <brueckner@linux.ibm.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Kim Phillips <kim.phillips@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/r/20190521030203.1447-1-vt@altlinux.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>