CTestCustom: Suppress warning matched on source file name

The `WarningMessagesDialog.cxx` source file name is displayed by
MSVC in the compiler output, and the CTest launcher matches the
name as a warning line starting in "Warning".  Suppress this
false positive with a custom exception.

CTestCustom.cmake.in

@@ -44,6 +44,7 @@ list(APPEND CTEST_CUSTOM_WARNING_EXCEPTION
   "Warning: LINN32: Last line.*is less.*"
   "Warning: Olimit was exceeded on function.*"
   "Warning: To override Olimit for all functions in file.*"
+  "WarningMessagesDialog\\.cxx"
   "warning.*directory name.*CMake-Xcode.*/bin/.*does not exist.*"
   "stl_deque.h:1051"
   "(Lexer|Parser).*warning.*conversion.*may (alter its value|change the sign)"