tools: fix SrcRemove on empty src

If the src is empty list, it will crash at:

    IndexError: list index out of range:
      File "/home/xxx/src/SConstruct", line 39:
        objs = PrepareBuilding(env, RTT_ROOT, has_libcpu=True)
      ...
      File "/home/xxx/src/drivers/SConscript", line 12:
        SrcRemove(src, src_need_remove)
      File "/home/rt-thread-stable/tools/building.py", line 496:
        if type(src[0]) == type('str'):

Commit d33df46f in master.

tools: preserve the order of CPPPATH/CPPDEFINES/LIBPATH/LIBS

The order of them are important while the uniqueness has nothing to do
with the compiling.

commit 2c5eea4c in upstream.

[stable] 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.

Commit b8bf6bef from master.

prepare RT-Thread 1.2.2 release

Merge 2.0.0 modification to prepare v1.2.2 release.

[mempool] reset the thread->error before suspending thread

Time out result and other errors is recorded in thread->error. Dirty
error will screw up the error handling code after the thread has been
wake up.

update the led driver.

[msh] don't complain on empty command

Just branch out and no complain on command length == 0;