[Libc][dlib] Auto remove macro _DLIB_THREAD_SUPPORT when IAR version higher than 8.20.1

components/libc/compilers/dlib/SConscript

 from building import *
+from distutils.version import LooseVersion
+from iar import IARVersion
+
 Import('rtconfig')
 
 src   = Glob('*.c')
@@ -11,7 +14,10 @@ CPPDEFINES = ['RT_USING_DLIBC']
 if rtconfig.PLATFORM == 'iar':
 
     if GetDepend('RT_USING_DFS'):
-        CPPDEFINES = CPPDEFINES + ['_DLIB_FILE_DESCRIPTOR', '_DLIB_THREAD_SUPPORT']
+        CPPDEFINES = CPPDEFINES + ['_DLIB_FILE_DESCRIPTOR']
+
+        if LooseVersion(IARVersion()) < LooseVersion("8.20.1"):
+            CPPDEFINES = CPPDEFINES + ['_DLIB_THREAD_SUPPORT']
 
     group = DefineGroup('dlib', src, depend = ['RT_USING_LIBC'], 
         CPPPATH = CPPPATH, CPPDEFINES = CPPDEFINES)