Tests: Add case for GENERATOR_IS_MULTI_CONFIG

Tests/RunCMake/get_property/IsMultiConfig-stdout.txt

@@ -0,0 +1 @@
+-- GENERATOR_IS_MULTI_CONFIG=1

Tests/RunCMake/get_property/IsMultiConfig.cmake

@@ -0,0 +1,2 @@
+get_property(is_multi_config GLOBAL PROPERTY GENERATOR_IS_MULTI_CONFIG)
+message(STATUS "GENERATOR_IS_MULTI_CONFIG=${is_multi_config}")

Tests/RunCMake/get_property/NotMultiConfig-stdout.txt

@@ -0,0 +1 @@
+-- GENERATOR_IS_MULTI_CONFIG=0

Tests/RunCMake/get_property/NotMultiConfig.cmake

@@ -0,0 +1 @@
+include(IsMultiConfig.cmake)

Tests/RunCMake/get_property/RunCMakeTest.cmake

@@ -22,3 +22,9 @@ run_cmake(NoTarget)
 run_cmake(NoSource)
 run_cmake(NoProperty)
 run_cmake(NoCache)
+
+if(RunCMake_GENERATOR MATCHES "Visual Studio|Xcode")
+  run_cmake(IsMultiConfig)
+else()
+  run_cmake(NotMultiConfig)
+endif()