[Analysis] Treat ldexpf() as missing on MinGW (#84748)

The function does exist, but it is a plain wrapper over regular ldexp(),
so there's no benefit in calling it over regular ldexp(). Therefore,
treat it as missing.

This fixes builds of Wine for aarch64 with Clang in mingw mode, which
regressed recently in 8d976c7f. That
commit unlocked transforming calls to ldexp into ldexpf, for some
codepaths within Wine. Wine can use compilers in mingw mode without
the regular mingw runtime libraries, which caused this to fail.
(However, if the transformation to use ldexpf() would have made sense,
the right fix would have been for Wine to provide a similar
ldexpf->ldexp wrapper just like mingw does.)