$OpenBSD: patch-include_json_config_h,v 1.4 2018/02/18 20:50:25 jca Exp $

"explicit" on non-constructors are a C++11 feature
https://github.com/open-source-parsers/jsoncpp/commit/04abe38148d99b2a5270521935115d769a714adc

Index: include/json/config.h
--- include/json/config.h.orig
+++ include/json/config.h
@@ -84,15 +84,23 @@
 #if __cplusplus >= 201103L
 # define JSONCPP_OVERRIDE override
 # define JSONCPP_NOEXCEPT noexcept
+# define JSONCPP_OP_EXPLICIT explicit
 #elif defined(_MSC_VER) && _MSC_VER > 1600 && _MSC_VER < 1900
 # define JSONCPP_OVERRIDE override
 # define JSONCPP_NOEXCEPT throw()
+# if _MSC_VER >= 1800 // MSVC 2013
+#  define JSONCPP_OP_EXPLICIT explicit
+# else
+#  define JSONCPP_OP_EXPLICIT
+# endif
 #elif defined(_MSC_VER) && _MSC_VER >= 1900
 # define JSONCPP_OVERRIDE override
 # define JSONCPP_NOEXCEPT noexcept
+# define JSONCPP_OP_EXPLICIT explicit
 #else
 # define JSONCPP_OVERRIDE
 # define JSONCPP_NOEXCEPT throw()
+# define JSONCPP_OP_EXPLICIT
 #endif
 
 #ifndef JSON_HAS_RVALUE_REFERENCES
