[iar] add CLOCKS_PER_SEC

https://www.iar.com/knowledge/learn/programming/using-c-standard-library-time-and-clock-functions/

components/libc/compilers/common/SConscript

@@ -9,6 +9,8 @@ CPPDEFINES = []
 
 if rtconfig.PLATFORM in ['armcc', 'armclang']:
     CPPDEFINES += ['__CLK_TCK=RT_TICK_PER_SECOND']
+elif rtconfig.PLATFORM == 'iar':
+    CPPDEFINES += ['CLOCKS_PER_SEC=RT_TICK_PER_SECOND'] # forcly revert to 1 by IAR
 
 src += Glob('*.c')