Fix for cyw43_wrappers.h build with C code (earlephilhower#2639)

Author: lyusupov

cores/rp2040/cyw43_wrappers.h

@@ -23,11 +23,15 @@
 #include <pico/cyw43_driver.h>
 
 extern bool __isPicoW;
+#ifdef __cplusplus
 extern "C" {
-    void init_cyw43_wifi();
-    void __lockBluetooth();
-    void __unlockBluetooth();
-    void cyw43_pinMode(pin_size_t pin, PinMode mode);
-    void cyw43_digitalWrite(pin_size_t pin, PinStatus val);
-    PinStatus cyw43_digitalRead(pin_size_t pin);
+#endif
+void init_cyw43_wifi();
+void __lockBluetooth();
+void __unlockBluetooth();
+void cyw43_pinMode(pin_size_t pin, PinMode mode);
+void cyw43_digitalWrite(pin_size_t pin, PinStatus val);
+PinStatus cyw43_digitalRead(pin_size_t pin);
+#ifdef __cplusplus
 }
+#endif