Export pgmspace symbols to C (esp8266#3955)

Author: bofh69

cores/esp8266/pgmspace.cpp

@@ -24,6 +24,8 @@
 #include <stdarg.h>
 #include "pgmspace.h"
 
+extern "C" {
+
 size_t strnlen_P(PGM_P s, size_t size) {
     const char* cp;
     for (cp = s; size != 0 && pgm_read_byte(cp) != '\0'; cp++, size--);
@@ -286,3 +288,5 @@ int vsnprintf_P(char* str, size_t strSize, PGM_P formatP, va_list ap) {
 
     return ret;
 }
+
+} // extern "C"

cores/esp8266/pgmspace.h

@@ -4,16 +4,14 @@
 #include <stdint.h>
 #include <stdio.h>
 
-#ifdef __ets__
-
 #ifdef __cplusplus
 extern "C" {
 #endif
+
+#ifdef __ets__
+
 #include "ets_sys.h"
 #include "osapi.h"
-#ifdef __cplusplus
-}
-#endif
 
 #define PROGMEM     ICACHE_RODATA_ATTR
 #define PGM_P  		const char *
@@ -136,4 +134,8 @@ static inline uint16_t pgm_read_word_inlined(const void* addr) {
 #define pgm_read_float_far(addr) 	pgm_read_float(addr)
 #define pgm_read_ptr_far(addr)		pgm_read_ptr(addr)
 
+#ifdef __cplusplus
+}
+#endif
+
 #endif //__PGMSPACE_H_