* A little easier to read the definition of the GPIO control macro for AVR.
No change in build result.
* Changed to not use GNU statement expression extension.
No change in build result.
* Modified split_common/serial.c to use qmk_firmware standard GPIO control macro.
No change in build result.
* fix PE6 -> E6
* remove some space
* add some comment to config_common.h
* Changed split_common/serial.c to use a newer version of qmk_firmware standard GPIO control macro.
1c5b0cbbeb