Add'l PLR options, AVR strstr_P compat (#13880)

Marlin/src/HAL/shared/Marduino.h

@@ -48,3 +48,10 @@
 #ifndef CBI
   #define CBI(A,B) (A &= ~(1 << (B)))
 #endif
+
+#ifndef __AVR__
+  #ifndef strchr_P // Some platforms define a macro (DUE, teensy35)
+    inline const char* strchr_P(const char *s, int c) { return strchr(s,c); }
+    //#define strchr_P(s,c) strchr(s,c)
+  #endif
+#endif