Tests: Fix RunCMake.FileAPI test with jsoncpp < 1.7.5

Prior to jsoncpp commit `126bdc2b05` (Reject extra chars if strictRoot,
2016-08-21, 1.7.5~2), it did not diagnose trailing characters in the
input after a JSON value.  Teach our corresponding test case to tolerate
the old behavior.

Tests/RunCMake/CMakeLists.txt

@@ -305,6 +305,9 @@ add_RunCMake_test(ExportImport)
 add_RunCMake_test(ExternalData)
 add_RunCMake_test(FeatureSummary)
 add_RunCMake_test(FPHSA)
+if(CMAKE_USE_SYSTEM_JSONCPP)
+  list(APPEND FileAPI_ARGS -DJsonCpp_VERSION_STRING=${JsonCpp_VERSION_STRING})
+endif()
 add_RunCMake_test(FileAPI -DPython_EXECUTABLE=${Python_EXECUTABLE}
                           -DCMAKE_CXX_COMPILER_ID=${CMAKE_CXX_COMPILER_ID})
 add_RunCMake_test(FindBoost)

Tests/RunCMake/FileAPI/ClientStateful-check.py

@@ -108,7 +108,11 @@ def check_query_json_empty(q):
     check_error_re(q, "value, object or array expected")
 
 def check_query_json_extra(q):
-    check_error_re(q, "Extra non-whitespace after JSON value")
+    if bool(os.environ.get("CMake_JSONCPP_PRE_1_7_5", "")) and is_dict(q) and sorted(q.keys()) == ["responses"]:
+        # jsoncpp < 1.7.5 did not diagnose extra non-whitespace characters
+        check_error(q["responses"], "'requests' member missing")
+    else:
+        check_error_re(q, "Extra non-whitespace after JSON value")
 
 def check_query_not_file(q):
     check_error_re(q, "failed to read from file")

Tests/RunCMake/FileAPI/RunCMakeTest.cmake

@@ -39,6 +39,10 @@ if(RunCMake_GENERATOR_IS_MULTI_CONFIG)
   set(RunCMake_TEST_OPTIONS "-DCMAKE_CONFIGURATION_TYPES=Debug\\;Release\\;MinSizeRel\\;RelWithDebInfo")
 endif()
 
+if(JsonCpp_VERSION_STRING AND JsonCpp_VERSION_STRING VERSION_LESS 1.7.5)
+  set(ENV{CMake_JSONCPP_PRE_1_7_5} 1)
+endif()
+
 run_cmake(Nothing)
 run_cmake(Empty)
 run_cmake(EmptyClient)