This used to work with the non-standard preprocessor in the older MSVC
versions, but doesn't work with the new standard-compliant one in MSVS
2022 (enabled by /Zc:preprocessor).
Luckily, it seems that we don't really need it neither, as simply
expanding the macros in a /-separated strings work with both the new and
the old preprocessors and has the same effect, so just do this instead.
Also simplify the code a little by defining wxTOOLKIT_FULL and
constructing wxSETUPH_PATH once instead of twice.
See #22654, #22680.
Co-Authored-By: Vadim Zeitlin <vadim@wxwidgets.org>
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