[compiler-rt] Fix extendhfxf2 test (PR #117665)

[Martin Storsjö via llvm-commits]

================
@@ -230,7 +230,7 @@ static inline double makeQNaN64(void)
     return fromRep64(0x7ff8000000000000UL);
 }
 
-#if __LDBL_MANT_DIG__ == 64 && defined(__x86_64__)
+#if HAS_80_BIT_LONG_DOUBLE
----------------
mstorsjo wrote:

FWIW, I also tested with an addition like this: https://github.com/mstorsjo/llvm-project/commit/de5ad3a19cf3c4d23bf1e338d27447d61f2eb731

That unbreaks the other unrelated tests, but this new test still is failing: https://github.com/mstorsjo/llvm-project/actions/runs/12026756315/job/33526363616

```
# | D:\a\llvm-project\llvm-project\compiler-rt\test\builtins\Unit\extendhfxf2_test.c:16:13: error: call to undeclared function 'compareResultF80'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
# |    16 |   int ret = compareResultF80(x, expectedHi, expectedLo);
# |       |             ^
```
So a similar condition would need to be added back to the condition within the actual test here as well.

https://github.com/llvm/llvm-project/pull/117665