check both for the full and the short name of the C++ ABI library, unset cache if the library is not usable

CMakeLists.txt

@@ -209,8 +209,8 @@ set_source_files_properties(
 
 
 function(test_cxx CXX_RUNTIME_NAME IS_STDLIB)
-	set(CXX_RUNTIME_NAME "${CMAKE_SHARED_LIBRARY_PREFIX}${CXX_RUNTIME_NAME}${CMAKE_SHARED_LIBRARY_SUFFIX}")
-	find_library(CXX_RUNTIME_LIB NAMES ${CXX_RUNTIME_NAME})
+	set(CXX_RUNTIME_NAME_FULL "${CMAKE_SHARED_LIBRARY_PREFIX}${CXX_RUNTIME_NAME}${CMAKE_SHARED_LIBRARY_SUFFIX}")
+	find_library(CXX_RUNTIME_LIB NAMES ${CXX_RUNTIME_NAME_FULL} ${CXX_RUNTIME_NAME})
 	if (CXX_RUNTIME_LIB)
 		message(STATUS "Testing ${CXX_RUNTIME_LIB} as the C++ runtime library")
 		if (ANDROID)
@@ -224,6 +224,8 @@ function(test_cxx CXX_RUNTIME_NAME IS_STDLIB)
 			CMAKE_FLAGS "-DCXX_RUNTIME=${CXX_RUNTIME_LIB}" ${CXX_RUNTIME_FLAGS})
 		if (USERUNTIME)
 			set(CXX_RUNTIME ${CXX_RUNTIME_LIB} PARENT_SCOPE)
+		else ()
+			unset(CXX_RUNTIME_LIB CACHE)
 		endif()
 	endif()
 endfunction()