To pick up the changes in:

  caabdd0f59a9771e ("ctype.h: remove duplicate isdigit() helper")

Addressing this perf build warning:

  Warning: Kernel ABI header at 'tools/include/linux/ctype.h' differs from latest version at 'include/linux/ctype.h'
  diff -u tools/include/linux/ctype.h include/linux/ctype.h

And we need to continue using the combination of:

  inline __isdigit()
  #define isdigit() __isdigit

When the __has_builtin() thing isn't available, as it is a builtin in
older systems with it as a builtin but with compilers not hacinv
__has_builtin(), rendering the __has_builtin() check useless otherwise.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

We got the sane_ctype.h headers from git and kept using it so far, but
since that code originally came from the kernel sources to the git
sources, perhaps its better to just use the one in the kernel, so that
we can leverage tools/perf/check_headers.sh to be notified when our copy
gets out of sync, i.e. when fixes or goodies are added to the code we've
copied.

This will help with things like tools/lib/string.c where we want to have
more things in common with the kernel, such as strim(), skip_spaces(),
etc so as to go on removing the things that we have in tools/perf/util/
and instead using the code in the kernel, indirectly and removing things
like EXPORT_SYMBOL(), etc, getting notified when fixes and improvements
are made to the original code.

Hopefully this also should help with reducing the difference of code
hosted in tools/ to the one in the kernel proper.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lkml.kernel.org/n/tip-7k9868l713wqtgo01xxygn12@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>