Updated teensy to use common code from stm directory.

Updated mconfigport.h to enable GC

Split stm/lexerstm.c/h into lexerstrc/h and lexerfatfs.c/h
Removed gchelper.s, malloc0.c printf.c string0.c from teensy
Added stubs for usart and lcd to teensy
Created teensy stub for lexerfatfs.c

Fixed teensy port to build with latest master.