Revert wxDO_LOG_IF_ENABLED() change for MSVC6 in r74735.

Revert wxDO_LOG_IF_ENABLED() change for MSVC6 in r74735.

The old solution worked fine for that compiler and the new one fails when
wxLogXXX() is used inside a switch statement to the wrong rules used by VC6
for the scope of the variables defined inside the for loop.

Simply revert back to using the old version for it, this will be easy to
re-revert after 3.0 by simply removing the check for it.

See #11829.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74762 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775