perl: update to 5.26.1

perl: update to 5.26.1

Required changes:

* Add qualifying '.' to scripts or to @INC, as appropriate since we're
  enabling default_inc_excludes_dot;

* Add new platform/library definitions like double-double format and
  locale library functions/headers;

* Delete patch 020 as it's been upstreamed;

Optional changes:

* Instead of using -@rm and having that fail, emit an error message,
  and be ignored, just use @rm -f instead which will always succeed.

Security
[CVE-2017-12837] Heap buffer overflow in regular expression compiler

Compiling certain regular expression patterns with the case-insensitive
modifier could cause a heap buffer overflow and crash perl. This has
now been fixed. [perl #131582]

[CVE-2017-12883] Buffer over-read in regular expression parser

For certain types of syntax error in a regular expression pattern, the
error message could either contain the contents of a random, possibly
large, chunk of memory, or could crash perl. This has now been fixed.
[perl #131598]

[CVE-2017-12814] $ENV{$key} stack buffer overflow on Windows

A possible stack buffer overflow in the %ENV code on Windows has been
fixed by removing the buffer completely since it was superfluous anyway.
[perl #131665]

Signed-off-by: Philip Prindeville <[email protected]>