[llvm] [clang] [ARM] .fpu equals fpv5-d16 disables floating point MVE which leads to unsupported MVE instructions assembler error for cortex M85/M55. (PR #71545)

[David Spickett via cfe-commits]

DavidSpickett wrote:

I think the commit title would make more sense at a glance if it was saying what is being done instead of what's being fixed. How about:
```
[llvm][ARM] Emit MVE .arch_extension after .fpu directive if it does not include MVE features
```
Then the commit message is fine as is, and tells the reader why this was done and what it fixes.

https://github.com/llvm/llvm-project/pull/71545