Use pkgconfig packed with debian jsoncpp instead

configure.ac

@@ -286,9 +286,10 @@ fi
 
 ### jsoncpp
 if test "x$ac_cv_want_fldigi" = "xyes"; then
-    AC_FLDIGI_JSONCPP
+    AC_FLDIGI_PKG_CHECK([jsoncpp], [jsoncpp >= 0.5], [no], [no])
 fi
 
+
 ### libssl
 if test "x$ac_cv_want_fldigi" = "xyes"; then
     AC_FLDIGI_PKG_CHECK([ssl], [libssl], [no], [no])

m4/jsoncpp.m4

@@ -1,11 +0,0 @@
-AC_DEFUN([AC_FLDIGI_JSONCPP], [
-    AC_LANG_PUSH([C++])
-    LIBS="$LIBS -ljsoncpp"
-    AC_MSG_CHECKING([for libjsoncpp])
-    AC_LINK_IFELSE(
-      [AC_LANG_PROGRAM([#include <jsoncpp/json.h>],
-        [Json::Value value(123); value = "test";])],
-      [AC_MSG_RESULT([yes])],
-      [AC_MSG_FAILURE([libjsoncpp is not installed.])])
-    AC_LANG_POP([C++])
-])