Merge pull request #9069 from Bob-the-Kuhn/broken-teensy

[2.0.x] fix Teensy2 compile error (PlatformIO LDF problem)

platformio.ini

@@ -195,6 +195,7 @@ board         = teensy20pp
 build_flags   = ${common.build_flags} -I $BUILDSRC_DIR
 #board_f_cpu  = 20000000L     ; Bug in Arduino framework disallows boards running at 20Mhz
 lib_deps      = ${common.lib_deps}
+lib_ldf_mode  = deep+
 src_filter    = ${common.default_src_filter}
 
 #