[BSP] fix LIBC options in stm32f7 rtconfig.h

bsp/stm32f7-disco/rtconfig.h

@@ -114,7 +114,7 @@
 
 // <section name="LIBC" description="C Runtime library setting" default="always" >
 // <bool name="RT_USING_LIBC" description="Using libc library" default="true" />
-#define RT_USING_NEWLIB
+#define RT_USING_LIBC
 // <bool name="RT_USING_PTHREADS" description="Using POSIX threads library" default="true" />
 //#define RT_USING_PTHREADS
 // </section>