qmk_firmware/tmk_core/common/progmem.h

#ifndef PROGMEM_H
#define PROGMEM_H 1

#if defined(__AVR__)
#   include <avr/pgmspace.h>
#else
#   define PROGMEM
#   define pgm_read_byte(p)     *((unsigned char*)p)
#   define pgm_read_word(p)     *((uint16_t*)p)
#   define pgm_read_dword(p)    *((uint32_t*)p)
#endif

#endif