Workaround strict-aliasing warnings

[Lauszus]

Also added missing pgm_read_ptr define

See: https://travis-ci.org/felis/USB_Host_Shield_2.0/jobs/328511332 and PaulStoffregen/cores@8a02ea6#diff-6e1ff9551639ac89d99617863bf84e10

[stickbreaker]

@Lauszus looks like it works! Here is my test code:

#include <pgmspace.h>
/* remove these comments to test new code
#undef pgm_read_word(addr)

#define pgm_read_word(addr) ({ \
  typeof(addr) _addr = (addr); \
  *(const unsigned short *)(_addr); \
})
*/
const PROGMEM  uint16_t charSet[]  = { 65000, 32796, 16843, 10, 11234};

const unsigned short sh=7;
void setup(){
  unsigned short a = pgm_read_word(&sh);
  Serial.begin(115200);
  Serial.printf(" a =%d\n",a);
  for(uint8_t b=0; b<(sizeof(charSet)/sizeof(uint16_t)); b++){
    a = pgm_read_word(&charSet[b]);
    Serial.printf(" a =%d\n",a);
    }
}

void loop(){}

output: with existing progmem

 a =7
 a =65000
 a =32796
 a =16843
 a =10
 a =11234

output: with proposed changes to progmem

 a =7
 a =65000
 a =32796
 a =16843
 a =10
 a =11234

Chuck.

[me-no-dev]

merged :)