[LR11x0] Add missing header for non-Arduino paltforms (#679)

src/modules/LR11x0/LR11x0.cpp

@@ -4,6 +4,7 @@
 #include "../../utils/Cryptography.h"
 
 #include <string.h>
+#include <math.h>
 
 #if !RADIOLIB_EXCLUDE_LR11X0