bug#66691: GnuTLS 3.8.1 fails to (cross-)build for GNU/Hurd

[Ludovic Courtès]

The recently-committed GnuTLS 3.8.1 fails to (cross-)build for GNU/Hurd:

--8<---------------cut here---------------start------------->8---
  CC       common.lo
  CC       key_encode.lo
  CC       key_decode.lo
  CC       time.lo
In file included from ./../system.h:47,
                 from ./../gnutls_int.h:85,
                 from common.c:24:
./../pathbuf.h:28:25: error: 'PATH_MAX' undeclared here (not in a function)
   28 | #define GNUTLS_PATH_MAX PATH_MAX
      |                         ^~~~~~~~
./../pathbuf.h:31:19: note: in expansion of macro 'GNUTLS_PATH_MAX'
   31 |         char base[GNUTLS_PATH_MAX + 1];
      |                   ^~~~~~~~~~~~~~~
In file included from ./../system.h:47,
                 from ./../gnutls_int.h:85,
                 from time.c:24:
./../pathbuf.h:28:25: error: 'PATH_MAX' undeclared here (not in a function)
   28 | #define GNUTLS_PATH_MAX PATH_MAX
      |                         ^~~~~~~~
./../pathbuf.h:31:19: note: in expansion of macro 'GNUTLS_PATH_MAX'
   31 |         char base[GNUTLS_PATH_MAX + 1];
      |                   ^~~~~~~~~~~~~~~
In file included from ./../system.h:47,
                 from ./../gnutls_int.h:85,
                 from key_decode.c:24:
./../pathbuf.h:28:25: error: 'PATH_MAX' undeclared here (not in a function)
   28 | #define GNUTLS_PATH_MAX PATH_MAX
      |                         ^~~~~~~~
./../pathbuf.h:31:19: note: in expansion of macro 'GNUTLS_PATH_MAX'
   31 |         char base[GNUTLS_PATH_MAX + 1];
      |                   ^~~~~~~~~~~~~~~
In file included from ./../system.h:47,
                 from ./../gnutls_int.h:85,
                 from key_encode.c:24:
./../pathbuf.h:28:25: error: 'PATH_MAX' undeclared here (not in a function)
   28 | #define GNUTLS_PATH_MAX PATH_MAX
      |                         ^~~~~~~~
./../pathbuf.h:31:19: note: in expansion of macro 'GNUTLS_PATH_MAX'
   31 |         char base[GNUTLS_PATH_MAX + 1];
      |                   ^~~~~~~~~~~~~~~
make[5]: *** [Makefile:2330: time.lo] Error 1
make[5]: *** Waiting for unfinished jobs....
make[5]: *** [Makefile:2330: common.lo] Error 1
make[5]: *** [Makefile:2330: key_decode.lo] Error 1
make[5]: *** [Makefile:2330: key_encode.lo] Error 1
make[5]: Leaving directory 
'/tmp/guix-build-gnutls-3.8.1.drv-0/gnutls-3.8.1/lib/x509'
--8<---------------cut here---------------end--------------->8---

This is because ‘PATH_MAX’ is undefined on GNU/Hurd.

Ludo’.