Merge pull request #4340 from mysterywolf/RT_TICK_PER_SECOND

[libc][keil] 在sconscript中定义CLOCKS_PER_SEC宏

components/libc/compilers/common/SConscript

@@ -16,7 +16,12 @@ else:
 if GetDepend('RT_USING_POSIX') == False:
         SrcRemove(src, ['unistd.c'])
 
+if rtconfig.CROSS_TOOL == 'keil':
+    CPPDEFINES = ['__CLK_TCK=RT_TICK_PER_SECOND']
+else:
+    CPPDEFINES = []
+
 if not GetDepend('RT_USING_MINILIBC') and (GetDepend('RT_USING_LIBC') or GetDepend('RT_LIBC_USING_TIME')):
-	group = DefineGroup('libc', src, depend = [''], CPPPATH = CPPPATH)
+    group = DefineGroup('libc', src, depend = [''], CPPPATH = CPPPATH, CPPDEFINES = CPPDEFINES)
 
 Return('group')