Remove CYGWIN condition to provide bswap16 fallback (#383)

src/modbus-data.c

@@ -54,7 +54,7 @@
 #  define bswap_16 _byteswap_ushort
 #endif
 
-#if !defined(__CYGWIN__) && !defined(bswap_16)
+#if !defined(bswap_16)
 #  warning "Fallback on C functions for bswap_16"
 static inline uint16_t bswap_16(uint16_t x)
 {