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

[Aaron Ballman via cfe-commits]

================
@@ -21,6 +25,7 @@ void a() {
   EVALF((2. + 3i) + (4. + 5i), 6. + 8i);
   EVALF((2. + 3i) - (4. + 5i), -2. - 2i);
   EVALF((2. + 3i) * (4. + 5i), -7. + 22i);
+  // div-precision-warning at +1 {{excess precision is requested but the target does not support excess precision which may result in observable differences in arithmetic behavior ,additional use of 'long double' were found but not diagnosed}}
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AaronBallman wrote:

This shows there's a formatting issue in the diagnostic because of:
```
behavior ,additional use
```

Also, I don't see any `long double` variables involved, these are all `double`. Are we passing in the wrong type or am I just blind?

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