It’s questionable that the SDL backend code is trying so hard to
maintain forbidden symbols at all since backend code is exactly
where such things are allowed, and it is a game of whack-a-mole
to keep system API changes from breaking this fragile system of
symbol redefinitions. Probably this should all just get replaced
with a FORBIDDEN_SYMBOL_ALLOW_ALL, but for the time being this at
least gets builds working again on up-to-date msys2/mingw-w64
compilers.
Fixes Trac#10405.