Fix

```
error: reinterpret_cast from 'const __FlashStringHelper *' (aka 'const __attribute__((address_space(1))) char *') to 'const char *' is not allowed
```

when compiling with Clang

Author: KOLANICH

Diff for: api/Print.cpp

@@ -41,7 +41,11 @@ size_t Print::write(const uint8_t *buffer, size_t size)
 size_t Print::print(const __FlashStringHelper *ifsh)
 {
 #if defined(__AVR__)
+  #if defined(__clang__)
+  PGM_P p = (PGM_P)(ifsh);
+  #else
   PGM_P p = reinterpret_cast<PGM_P>(ifsh);
+  #endif
   size_t n = 0;
   while (1) {
     unsigned char c = pgm_read_byte(p++);