Detect <codecvt> header automatically

ConfigureChecks.cmake

@@ -14,6 +14,13 @@ else()
 	set(HAVE_ZLIB 0)
 endif()
 
+# Determine whether your compiler supports codecvt header.
+
+check_cxx_source_compiles("
+	#include <codecvt>
+	int main() { std::codecvt_utf8_utf16<wchar_t> x; return 0; }
+" HAVE_CODECVT)
+
 set(CMAKE_MODULE_PATH ${CMAKE_CURRENT_SOURCE_DIR}/cmake/modules)
 find_package(CppUnit)
 if(NOT CppUnit_FOUND AND BUILD_TESTS)