Merge pull request #118 from UncleRus/core/gpio_cpp_fix

esp/gpio.h c++ linker compatibility

core/include/esp/gpio.h

@@ -13,6 +13,10 @@
 #include "esp/iomux.h"
 #include "esp/interrupts.h"
 
+#ifdef	__cplusplus
+extern "C" {
+#endif
+
 typedef enum {
     GPIO_INPUT,
     GPIO_OUTPUT,         /* "Standard" push-pull output */
@@ -139,4 +143,8 @@ static inline gpio_inttype_t gpio_get_interrupt(const uint8_t gpio_num)
     return (gpio_inttype_t)FIELD2VAL(GPIO_CONF_INTTYPE, GPIO.CONF[gpio_num]);
 }
 
+#ifdef	__cplusplus
+}
+#endif
+
 #endif