Core: Fix msvc warning about strdup being deprecated

"warning: C4996: 'strdup': The POSIX name for this item is deprecated.
Instead, use the ISO C++ conformant name: _strdup."

Change-Id: Ic2335664c4d2baf74eaa201ba4a85e8af3575bfb
Reviewed-by: Eike Ziller <eike.ziller@nokia.com>

src/plugins/coreplugin/id.cpp

@@ -106,7 +106,7 @@ static int theId(const char *str)
         if (lastUid == 0)
             stringFromId.append(QByteArray());
         res = ++lastUid;
-        sh.str = strdup(sh.str);
+        sh.str = qstrdup(sh.str);
         idFromString[sh] = res;
         stringFromId.append(QByteArray::fromRawData(sh.str, sh.n));
     }