add libc in link when enable RT_USING_NEWLIB

components/libc/newlib/SConscript

@@ -8,14 +8,14 @@ if GetDepend('RT_USING_NEWLIB') and rtconfig.CROSS_TOOL != 'gcc':
     exit(0)
 
 cwd = GetCurrentDir()
-src	= Glob('*.c')
+src = Glob('*.c')
 CPPPATH = [cwd]
 
-# link with libm in default.
+# link with libc and libm:
 # libm is a frequently used lib. Newlib is compiled with -ffunction-sections in
 # recent GCC tool chains. The linker would just link in the functions that have
 # been referenced. So setting this won't result in bigger text size.
-LIBS = ['m']
+LIBS = ['c', 'm']
 
 group = DefineGroup('newlib', src, depend = ['RT_USING_NEWLIB'],
                     CPPPATH = CPPPATH, LIBS = LIBS)