[clang] Silence -Wcast-function-type warnings on idiomatic Windows code (PR #135660)

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

> LGTM. Or should I say, "Thanks, I hate it".
> 
> Do you know how likely it is WG14 come up with a good solution for "arbitrary function pointer" ?

The last we heard on this topic was https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2230.htm which was discussed in Brno in 2018 and the following is from my notes: We had consensus that the overall idea of a generic function pointer type is a good one. We took a straw poll to determine whether this should be a core language feature: F:14/O:0/A:5, which is strong consensus for a language feature rather than library option.

So we need an updated paper (the author of that paper retired from the committee).

https://github.com/llvm/llvm-project/pull/135660