[clang] [NFC] Move warning from CodeGen to Sema. (PR #107397)

[Aaron Ballman via cfe-commits]

================
@@ -6784,6 +6784,11 @@ def warn_arc_lifetime_result_type : Warning<
   "ARC %select{unused|__unsafe_unretained|__strong|__weak|__autoreleasing}0 "
   "lifetime qualifier on return type is ignored">,
   InGroup<IgnoredQualifiers>;
+def warn_excess_precision_not_supported : Warning<
+  "excess precision is requested but the target does not support excess "
+  "precision %select{which may result in observable differences in arithmetic "
+  "behavior}0 %select{|,additional use of %1 were found but not diagnosed}2">,
----------------
AaronBallman wrote:

```suggestion
  "behavior}0 %select{|,additional uses of %1 were found but not diagnosed}2">,
```

https://github.com/llvm/llvm-project/pull/107397