The rt_list_isempty has prototype of "int rt_list_isempty(const rt_list_t *l)".
So the compiler has a good reason that the rt_thread_defunct list does
not change within rt_thread_idle_excute thus optimize the "while" loop
into a "if".

So add the volatile qualifier when test against the rt_thread_defunc list.

[Serial] BUG Fix: data be send twice in mode that other than polling

minilibc: define SIZE_MAX in stdint.h

tools/building: remove the use of startupinfo

The startupinfo does not have any visible effects on the building
process and some old Python version does not have it at all. So remove
it for the seek of simple.

Tested `scons -j4` in a dual core virtual machine.

Add conditional compilation about IPv6 sources and headers, change code style

correct netconn API usage

fix:comment spelling mistake

[net] Add lwIP head porting to fetch lwIP new feature, for example IPv4/v6 dual stack.

tools/keil: preserve the order of CPPPATH

The order of CPPPATH is important: some project would use the order of
CPPPATH to override the default configuration headers. This commit also
refine the this piece of code in a more Pythonic way.

[finsh] fixed finsh issue.

relation=>relocation

kernel: mempool: fix race condition in rt_mp_alloc

When thread wake up from waiting for memory, there is a chance that
there is no memory available in high pressure. So use a loop to check
again. Otherwise, there will be a NULL reference.

Ls1b

[BSP]BM9BF618S:fix timer initialization issue.