Support 'info proc' for FreeBSD process core dumps.

Support 'info proc' for FreeBSD process core dumps.

- Command line arguments are obtained from the pr_psargs[] array
  saved in the NT_PRPSINFO note.
- The 'cwd' and 'exe' values are obtained from the per-process file
  descriptor table stored in the NT_PROCSTAT_FILES core note.
- 'mappings' is implemented by walking the array of VM map entries
  stored in the NT_PROCSTAT_VMMAP core note.
- 'status' output is generated by outputting fields from
  the first structure stored in the NT_PROCSTAT_PROC core note.
- 'stat' is aliased to 'status'.

gdb/ChangeLog:

	* fbsd-tdep.c (KVE_STRUCTSIZE, KVE_START, KVE_END, KVE_OFFSET)
	(KVE_FLAGS, KVE_PROTECTION, KVE_PATH, KINFO_VME_PROT_READ)
	(KINFO_VME_PROT_WRITE, KINFO_VME_PROT_EXEC, KINFO_VME_FLAG_COW)
	(KINFO_VME_FLAG_NEEDS_COPY, KINFO_VME_FLAG_NOCOREDUMP)
	(KINFO_VME_FLAG_SUPER, KINFO_VME_FLAG_GROWS_UP)
	(KINFO_VME_FLAG_GROWS_DOWN, KF_STRUCTSIZE, KF_TYPE, KF_FD)
	(KF_PATH, KINFO_FILE_TYPE_VNODE, KINFO_FILE_FD_TYPE_CWD)
	(KINFO_FILE_FD_TYPE_TEXT, SIG_WORDS, struct kinfo_proc_layout)
	(kinfo_proc_layout_32, kinfo_proc_layout_i386)
	(kinfo_proc_layout_64, fbsd_vm_map_entry_flags)
	(fbsd_core_info_proc_mappings, fbsd_core_vnode_path)
	(fbsd_core_fetch_timeval, fbsd_print_sigset)
	(fbsd_core_info_proc_status, fbsd_core_info_proc): New.
	(fbsd_init_abi):  Install gdbarch "core_info_proc" method.
	* fbsd-tdep.h (fbsd_vm_map_entry_flags): New.