libjq: extern C for C++

If using libjq from C++ it would be nice to not need to do this at the
import site, so just extern "C" to the public headers for libjq

Signed-off-by: Tyler Rockwood <rockwood@redpanda.com>

src/jq.h

@@ -4,6 +4,10 @@
 #include <stdio.h>
 #include "jv.h"
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 enum {
   JQ_DEBUG_TRACE = 1,
   JQ_DEBUG_TRACE_DETAIL = 2,
@@ -69,4 +73,8 @@ jv jq_util_input_get_current_line(jq_state*);
 
 int jq_set_colors(const char *);
 
+#ifdef __cplusplus
+}
+#endif
+
 #endif /* !JQ_H */