- fix build error

  brk.c:(.text.__GI_sysconf+0xd4): undefined reference to `clock_getres'

libc/unistd/sysconf.c

@@ -884,7 +884,7 @@ long int sysconf(int name)
 #endif
 
     case _SC_MONOTONIC_CLOCK:
-#ifdef __NR_clock_getres
+#if defined __UCLIBC_HAS_REALTIME__ && defined __NR_clock_getres
       /* Check using the clock_getres system call.  */
       if (clock_getres(CLOCK_MONOTONIC, NULL) >= 0)
         return _POSIX_VERSION;