* ports/unix/sys_arch.c, ports/unix/include/arch/cc.h,
ports/unix/netif/tcpdump.c, ports/unix/proj/unixsim/simhost.c:
Fix 64-bit issues in unix port.
* ports/unix/include/arch/cc.h: silence warning about packed
attribute on fields, since whole struct is packed.
* ports/unix/proj/unixsim/apps/shell.c: Remove rexmit fields
from stat data, in line with lwip stats changes.
Applied a patch from Marc Boucher which has the following changes:
1) Fixed sys_arch.txt documentation to have new return type from
sys_thread_new.
2) Removed unnecessary casts on calling sys_timeout() in certain files.
3) Removed some unnecessary break statements after return statements.
4) Changed sys_timeout_remove() to sys_untimeout().
5) Added some forgotten #ifndef SYS_LIGHTWEIGHT_PROT to memp.c
6) Changed LWIP_DIAG and LWIP_PLATFORM_ASSERT to have do while().
