Use standard CMake variables - static/shared lib.

Replace JSONCPP_LIB_BUILD_SHARED => BUILD_SHARED_LIBS
diff --git a/devtools/agent_vmxp.json b/devtools/agent_vmxp.json
index 61f5a4c..997aa5e 100644
--- a/devtools/agent_vmxp.json
+++ b/devtools/agent_vmxp.json
@@ -12,8 +12,8 @@
         },

         {"name": "shared_dll",

          "variables": [

-            ["JSONCPP_LIB_BUILD_SHARED=true"],

-            ["JSONCPP_LIB_BUILD_SHARED=false"]

+            ["BUILD_SHARED_LIBS=true"],

+            ["BUILD_SHARED_LIBS=false"]

           ]

         },

         {"name": "build_type",