[clang] [llvm] Add f8E4M3 IEEE 754 type to llvm (PR #97179)

[Matt Arsenault via cfe-commits]

arsenm wrote:

Title and description needs rewording. This isn't adding the type "to llvm" which would imply adding the IR type, but only to APFloat 

https://github.com/llvm/llvm-project/pull/97179