NSH: Add a break command; if-then-else and looping behavior can not be configured out of the build for small systems that need minimal scripting capability

nshlib/nsh_script.c

@@ -129,10 +129,11 @@ int nsh_script(FAR struct nsh_vtbl_s *vtbl, FAR const char *cmd,
 
       do
         {
-          /* Get the next line of input from the file */
+          /* Flush any output generated by the previous line */
 
           fflush(stdout);
 
+#ifndef CONFIG_NSH_DISABLE_LOOPS
           /* Get the current file position.  This is used to control
            * looping.  If a loop begins in the next line, then this file
            * offset will be needed to locate the top of the loop in the
@@ -146,6 +147,7 @@ int nsh_script(FAR struct nsh_vtbl_s *vtbl, FAR const char *cmd,
             {
               nsh_output(vtbl, g_fmtcmdfailed, "loop", "ftell", NSH_ERRNO);
             }
+#endif
 
           /* Now read the next line from the script file */