[libunwind] [libunwind][MIPS] Add o32 single-float support (PR #218994)

[Saleem Abdulrasool via cfe-commits]

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@@ -3101,7 +3112,14 @@ inline bool Registers_mips_o32::validRegister(int regNum) const {
 inline uint32_t Registers_mips_o32::getRegister(int regNum) const {
   if (regNum >= UNW_MIPS_R0 && regNum <= UNW_MIPS_R31)
     return _registers.__r[regNum - UNW_MIPS_R0];
-#if defined(__mips_hard_float) && __mips_fpr == 32
+#if defined(__mips_hard_float) && defined(__mips_single_float)
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compnerd wrote:

I wonder if it might be better to fold the conditions:

```cpp
#if defined(__mips_hard_float)
#if defined(__mips_single_float)
#elif __mips_fpr == 32
#endif
#endif
```

https://github.com/llvm/llvm-project/pull/218994