[llvm] Update the EBO static_assert to dheck against APFloat::Storage instead of IEEEFloat. (PR #112589)

[Daniel Chen via llvm-commits]

================
@@ -99,6 +99,11 @@ enum class fltNanEncoding {
   NegativeZero,
 };
 
+class APFloatEBOChecker {
----------------
DanielCChen wrote:

The reason is that `APFloat::U` is private, so we added a `friend` class to access it.

https://github.com/llvm/llvm-project/pull/112589