[libc] [llvm] [libc] Add proxy header for float.h. (PR #93504)

[Nick Desaulniers via llvm-commits]

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@@ -32,9 +17,9 @@
 #define FLT_EVAL_METHOD __FLT_EVAL_METHOD__
 #endif // FLT_EVAL_METHOD
 
-#ifndef DECIMAL_DIG
-#define DECIMAL_DIG __DECIMAL_DIG__
-#endif // DECIMAL_DIG
+#ifndef FLT_ROUNDS
+#define FLT_ROUNDS 1
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nickdesaulniers wrote:

Or define as:

```suggestion
#define FLT_ROUNDS FLT_TONEAREST
```

https://github.com/llvm/llvm-project/pull/93504