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

[B I Mohammed Abbas 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
----------------
biabbas wrote:

Yeah, https://github.com/mstorsjo/llvm-project/actions/runs/12026429539/job/33525399943 this suggests uint128t is not defined, thus this should be only enabled for x86_64.
Alternatively we could check if __uint128t is available with check_c_source_compiles and we can add another flag like we do here https://github.com/llvm/llvm-project/blob/f082782c1b3ec98f50237ddfc92e6776013bf62f/compiler-rt/lib/builtins/CMakeLists.txt#L873.

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