[compiler-rt] [builtins] Avoid using long double in generic sources (PR #69754)

[Alexander Richardson via llvm-commits]

arichardson wrote:

> This seems to not build on Windows, at least with clang-cl as host compiler: http://45.33.8.238/win/85105/step_4.txt
> 
> Could you take a look?

My guess is that HAS_80_BIT_LONG_DOUBLE is not being defined for some reason?

```
#if (defined(__i386__) || defined(__x86_64__)) &&                              \
    !(defined(_MSC_VER) || defined(__ANDROID__))
#define HAS_80_BIT_LONG_DOUBLE 1
#elif defined(__m68k__) || defined(__ia64__)
#define HAS_80_BIT_LONG_DOUBLE 1
#else
#define HAS_80_BIT_LONG_DOUBLE 0
#endif

#if HAS_80_BIT_LONG_DOUBLE
```

https://github.com/llvm/llvm-project/pull/69754