sim: mark header that need to be as C header

sim/portmacro_cmsis.h

@@ -29,6 +29,10 @@
 #ifndef PORTMACRO_CMSIS_H
 #define PORTMACRO_CMSIS_H
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 #include <stdint.h>
 
 typedef uint32_t TickType_t;
@@ -46,4 +50,8 @@ const NRF_RTC_Type portNRF_RTC_REG = 1;
 
 void portYIELD_FROM_ISR(BaseType_t);
 
+#ifdef __cplusplus
+}
+#endif
+
 #endif /* PORTMACRO_CMSIS_H */