[compiler-rt] [builtins] Support building the 128-bit float functions on i386 (PR #122658)

[Alexander Richardson via llvm-commits]

================
@@ -12,7 +12,8 @@
 #define QUAD_PRECISION
 #include "fp_lib.h"
 
-#if defined(CRT_HAS_TF_MODE) && __LDBL_MANT_DIG__ == 64 && defined(__x86_64__)
+#if defined(CRT_HAS_TF_MODE) && __LDBL_MANT_DIG__ == 64 &&                     \
----------------
arichardson wrote:

This should actually be checking `HAS_80_BIT_LONG_DOUBLE`, which is set correctly depending on environments that support it: https://github.com/llvm/llvm-project/blob/4a4a8a1476b1386b523dc5b292ba9a5a6748a9cf/compiler-rt/lib/builtins/int_types.h#L158
```suggestion
#if defined(CRT_HAS_TF_MODE) && HAS_80_BIT_LONG_DOUBLE
```

https://github.com/llvm/llvm-project/pull/122658