Fixed IAR serial fgets fgetc

IAR's Dlib has some problems with unbuffered stream, however I found a workaround. setvbuf with these params generate a buffer with size 1. 
+        _file->_Mode = (unsigned short)(_file->_Mode & ~ 0x1000);/* Unset read mode */
Is to remove read mode from _file after read because writes will otherwise be blocked.
+        _file->_Rend = _file->_Wend;
+        _file->_Next = _file->_Wend;
If this is not set the last char from fgets will be rewritten next time (saved in buffer). So for instance if you send a \n to end a string sequence it would be a double new line. The other new line would be written as start  of the next string.