Update SdFat to not undefine F() macro

earlephilhower · earlephilhower · commit 6dd3d2d560c2 · 2019-11-15T17:12:30.000-08:00
Fixes esp8266#6767 . Remove the `undef F` from SysCall.h as it is not needed nor used in the SD or SDFS libraries. This puts F() strings back in flash when using the SD/SDFS libs.
diff --git a/libraries/ESP8266SdFat b/libraries/ESP8266SdFat
@@ -1 +1 @@
-Subproject commit af4ed0c5ec3084cb3883df51ec2052791ca2bff2
+Subproject commit b240d2231a117bbd89b79902eb54cae948ee2f42
