Tests: Add missing include for MSVC

Change-Id: I95196a8d57a8bf8f09a52aa54fa1c8bbfe752168
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>

tests/auto/debugger/tst_namedemangler.cpp

@@ -32,6 +32,8 @@
 #include <QObject>
 #include <QTest>
 
+#include <cctype>
+
 #define TEST_CORRECTLY_MANGLED_NAME(mangled, expectedDemangled) \
     do { \
         QVERIFY2(demangler.demangle(QLatin1String(mangled)), qPrintable(demangler.errorString())); \