[clang] [PPC] Disable vsx and altivec when -msoft-float is used (PR #100450)

[Chen Zheng via cfe-commits]

https://github.com/chenzheng1030 commented:

Compared with `llvm/lib/Target/PowerPC/PPC.td`, seems still miss below implicit flag:
`crypto`

```
def FeatureP8Crypto : SubtargetFeature<"crypto", "HasP8Crypto", "true",
                                       "Enable POWER8 Crypto instructions",
                                       [FeatureP8Altivec]>;
```

Other implications from `hard-float` are all covered in this patch.

https://github.com/llvm/llvm-project/pull/100450