[parrot/parrot] 3a0f86: [gc] fix SIGBUS on arm

[GitHub]

  Branch: refs/heads/smoke-me/gc-ptrdiff-gh1200
  Home:   https://github.com/parrot/parrot
  Commit: 3a0f86a835bbfd07d3104c65902743758363c93e
      https://github.com/parrot/parrot/commit/3a0f86a835bbfd07d3104c65902743758363c93e
  Author: Reini Urban <rurban at cpanel.net>
  Date:   2015-02-04 (Wed, 04 Feb 2015)

  Changed paths:
    M src/gc/system.c

  Log Message:
  -----------
  [gc] fix SIGBUS on arm

Apparently gcc on arm-openbsd5.6 threats ptrdiff_t cur_var_ptr++
in a for loop of size 1 not 4. But this is not a char*!
We better use size_t uniformly for our pointers values.

Should fix GH #1200.