[demangler][LoongArch] Correct the mangled_size for long double

[SixWeining]

Summary

The size of long double in LoongArch (both LA32 and LA64) is 16 bytes, thus
the mangled_size should be 32.

This is same as RISCV's change in D126480.

[xen0n]

I have made the same change locally but your commit message is somewhat better than mine in that it provides a bit more context. I'll rebase on top of this change then. Thanks!

[SixWeining]

Can a libc++ approver take a look? Thanks.

libcxxabi/src/demangle/ItaniumDemangle.h

struct FloatData<double>
     static const size_t max_demangled_size = 32;
     static constexpr const char* spec = "%a";
 };
 
 template <>
 struct FloatData<long double>
 {
 #if defined(__mips__) && defined(__mips_n64) || defined(__aarch64__) || \
-    defined(__wasm__) || defined(__riscv)
+    defined(__wasm__) || defined(__riscv) || defined(__loongarch__)
     static const size_t mangled_size = 32;
 #elif defined(__arm__) || defined(__mips__) || defined(__hexagon__)
     static const size_t mangled_size = 16;
 #else
     static const size_t mangled_size = 20;  // May need to be adjusted to 16 or 24 on other platforms
 #endif
     // `-0x1.ffffffffffffffffffffffffffffp+16383` + 'L' + '\0' == 42 bytes.
     // 28 'f's * 4 bits == 112 bits, which is the number of mantissa bits.

llvm/include/llvm/Demangle/ItaniumDemangle.h

struct FloatData<double>
     static const size_t max_demangled_size = 32;
     static constexpr const char* spec = "%a";
 };
 
 template <>
 struct FloatData<long double>
 {
 #if defined(__mips__) && defined(__mips_n64) || defined(__aarch64__) || \
-    defined(__wasm__) || defined(__riscv)
+    defined(__wasm__) || defined(__riscv) || defined(__loongarch__)
     static const size_t mangled_size = 32;
 #elif defined(__arm__) || defined(__mips__) || defined(__hexagon__)
     static const size_t mangled_size = 16;
 #else
     static const size_t mangled_size = 20;  // May need to be adjusted to 16 or 24 on other platforms
 #endif
     // `-0x1.ffffffffffffffffffffffffffffp+16383` + 'L' + '\0' == 42 bytes.
     // 28 'f's * 4 bits == 112 bits, which is the number of mantissa bits.