COMP: Ignore warning LNK4204 for CMake dashboard

This warning appears for libtar.obj, curltest.obj, and synch_client.obj
regularly on CMake dashboard submissions from VS builds.  They seem to
occur due to some kind of race condition for objects in small targets.
There is nothing wrong with the code, so this just suppresses the
warnings.

CTestCustom.cmake.in

@@ -2,6 +2,7 @@ SET(CTEST_CUSTOM_WARNING_EXCEPTION
   ${CTEST_CUSTOM_WARNING_EXCEPTION}
   "xtree.[0-9]+. : warning C4702: unreachable code"
   "warning LNK4221"
+  "warning LNK4204" # Occurs by race condition with objects in small libs
   "variable .var_args[2]*. is used before its value is set"
   "jobserver unavailable"
   "warning: \\(Long double usage is reported only once for each file"