Update Adafruit_GFX.cpp

[mroobol6]

*** CHANGED ***
#ifndef pgm_read_byte
#define pgm_read_byte(addr) (*(const unsigned char *)(addr)) #endif

*** TO - for use in Particle Photon ***
// #ifndef pgm_read_byte
#undef pgm_read_byte
#define pgm_read_byte(addr) (*(const unsigned char *)(addr)) // #endif

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[mroobol6]

approve

[BillyDonahue]

This would break Arduino AVR, historically the most important platform for GFX.

This change is undefining special macros that the system headers (implicitly included by Arduino AVR) would have defined. The existing code would only define these macros if the system had not yet done so, and so it defined them with a cast that didn't consider PROGMEM storage.

PS: Title and description should be updated as well, per the boilerplate guidance.