halcmd: Make headers usable from C++

Signed-off-by: Jeff Epler <jepler@unpythonic.net>

Author: jepler

src/hal/utils/halcmd.h

@@ -41,6 +41,9 @@
 #define HALCMD_H
 #include <stdio.h>
 #include "hal.h"
+
+RTAPI_BEGIN_DECLS
+
 extern int halcmd_startup(int quiet);
 extern void halcmd_shutdown();
 extern int halcmd_parse_cmd(char * tokens[]);
@@ -91,4 +94,6 @@ extern FILE *halcmd_inifile;
 #define MAX_CMD_LEN 1024
 #define MAX_EXPECTED_SIGS 999
 
+RTAPI_END_DECLS
+
 #endif