[compiler-rt] Add extendhfxf2 into compiler rt (PR #113897)

[Alexander Richardson via llvm-commits]

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@@ -0,0 +1,16 @@
+//===-- lib/extendhfxf2.c - half -> long double conversion --------*- C -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#define SRC_HALF
+#define DST_DOUBLE
+#include "fp_extend_impl.inc"
+
+// Long double are expected to be as precise as double.
+COMPILER_RT_ABI NOINLINE long double __extendhfxf2(src_t a) {
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arichardson wrote:

```suggestion
COMPILER_RT_ABI NOINLINE xf_float __extendhfxf2(src_t a) {
```

https://github.com/llvm/llvm-project/pull/113897