Add missing extern "C" to header files (closes #104)

src/rp2_common/hardware_resets/include/hardware/resets.h

@@ -56,6 +56,10 @@
  * \include hello_reset.c
  */
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 /// \tag::reset_funcs[]
 
 /*! \brief Reset the specified HW blocks
@@ -88,4 +92,8 @@ static inline void unreset_block_wait(uint32_t bits) {
 }
 /// \end::reset_funcs[]
 
+#ifdef __cplusplus
+}
+#endif
+
 #endif