Unify disabling build of llvm related plugins or test on Windows

If libclang's build mode mismatches the current build mode
of Qt Creator some plugins are automatically disabled.
Do the same for the unittest and unify the way to do this.

Change-Id: Ib4cd6494ed63cb89ed8d99b3c0ba23a19572fc9b
Reviewed-by: Marco Bubke <marco.bubke@qt.io>

src/plugins/clangrefactoring/clangrefactoring.pro

@@ -6,11 +6,6 @@ include(../../shared/clang/clang_defines.pri)
 
 requires(!isEmpty(LIBTOOLING_LIBS))
 
-win32 {
-    LLVM_BUILDMODE = $$system($$llvm_config --build-mode, lines)
-    CONFIG(debug, debug|release):requires(equals(LLVM_BUILDMODE, "Debug"))
-}
-
 HEADERS += \
     clangrefactoringplugin.h \
     baseclangquerytexteditorwidget.h \