[Checkins] [zopefoundation/persistent] dc261e: Fix C compilation warning

[Marius Gedminas]

  Branch: refs/heads/fix-c-warning
  Home:   https://github.com/zopefoundation/persistent
  Commit: dc261e61494731c233700a355673bc2901f7baec
      https://github.com/zopefoundation/persistent/commit/dc261e61494731c233700a355673bc2901f7baec
  Author: Marius Gedminas <marius at gedmin.as>
  Date:   2019-04-25 (Thu, 25 Apr 2019)

  Changed paths:
    M persistent/cPersistence.c

  Log Message:
  -----------
  Fix C compilation warning

gcc 8.3.0 emits this during python setup.py build:

persistent/cPersistence.c: In function ‘Per_repr’:
persistent/cPersistence.c:1481:44: warning: format ‘%llx’ expects argument of type ‘long long unsigned int’, but argument 4 has type ‘uint64_t’ {aka ‘long unsigned int’} [-Wformat=]
         snprintf(buf, sizeof(buf) - 1, "%llx", oid_value);
                                         ~~~^   ~~~~~~~~~
                                         %lx

<stdint.h> defines standard macros such as PRId64, PRIu64 and PRIx64 for
printing {u,}int64_t values, so let's use them.