[PATCH] QProcess/Unix: fallback on _POSIX_PIPE_BUF w/ missing PIPE_BUF

[PATCH] QProcess/Unix: fallback on _POSIX_PIPE_BUF w/ missing PIPE_BUF

PIPE_BUF is optional in POSIX, e.g. "where the corresponding value is
equal to or greater than the stated minimum, but where the value can
vary depending on the file to which it is applied." [1]

GNU/Hurd does not provide PIPE_BUF, so fallback to its minimum
acceptable value, that is _POSIX_PIPE_BUF.

[1] https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/limits.h.html

Also, explicitly include <limits.h> in this file, to make sure PIPE_BUF
or _POSIX_PIPE_BUF are available without relying on other headers to
pull <limits.h>.

Change-Id: Ifae964db81841e1d31fc09e73b45594af9a326d1
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Gbp-Pq: Name upstream_QProcess-Unix-fallback-on-_POSIX_PIPE_BUF-w-missing-.patch