[clang] Honor pragmas with -ffp-contract=fast, depecate fast-honor-pragmas (PR #105746)

[Andy Kaylor via cfe-commits]

andykaylor wrote:

> Hello @andykaylor ,
> 
> I am working on this pragma operation, with a different scenario. For example: https://godbolt.org/z/nTfYW64j4
> 
> Is it ok to merge this patch?

As mentioned [here](https://discourse.llvm.org/t/rfc-honor-pragmas-with-ffp-contract-fast/80797/14), I ran into some problems with inconsistent handling of contract in the backends. There have been some changes in that respect but I don't think the  problems are entirely resolved.

There's a bit more discussion here: https://discourse.llvm.org/t/allowfpopfusion-vs-sdnodeflags-hasallowcontract/80909

https://github.com/llvm/llvm-project/pull/105746