Prevent mangling of symbols when linking with C++

Signed-off-by: Jakub Pawlo <jakubpawlo@gmail.com>
Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

include/editline.h

@@ -29,6 +29,10 @@
 #define ISMETA(x)       ((x) & 0x80)
 #define UNMETA(x)       ((x) & 0x7F)
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 /* Command status codes. */
 typedef enum {
     CSdone = 0,                 /* OK */
@@ -100,4 +104,8 @@ void rl_deprep_terminal(void);
 
 int rl_getc(void);
 
+#ifdef __cplusplus
+}
+#endif
+
 #endif  /* __EDITLINE_H__ */