[X86] Generated Binary Crash Unless `-disable-postra-machine-sink` Specified

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Given this code:

```cpp
#include
#include
#include

struct Parser
{
virtual int Put(std::span, char *)
{
return 0;
}

virtual void Finish()
{
throw 1;
}

virtual bool Complete() const noexcept
{
return false;
}

virtual bool Status() const
{
return true;
}

std::string Decode(std::span input);
};

std::string Parser::Decode(std::span input)
{
char chunk[1]{};
std::string body;
unsigned offset = 0;
while (true)
{
if (offset == input.size())
{
Finish();
}
else if (!Complete())
{
const auto progress = Put(input.subspan(offset), chunk);
offset += progress;
body.append(chunk, 1);
}
const auto status = Status();
if (!status)
{
continue;
}
return body;
}
}

int main()
{
Parser parser;
// Keep the virtual calls in Decode opaque without compiler-specific attributes.
try
{
volatile auto decode = &Parser::Decode;
(void)(parser.*decode)({});
}
catch (int error)
{
std::printf("Caught %d\n", error);
return error == 1 ? 0 : 1;
}
return 2;
}
```

When compiled for `x86` at `-O2`, the generated binary segfaults: https://godbolt.org/z/z4Mq4jnqW

These configurations are known **not** to fail:
- Other architectures (`x86_64`, `aarch64`) at `-O2`.
- `x86` at `-O0`.
- `x86` at `-O2`, but with `-mllvm -disable-postra-machine-sink`.
- `x86` at `-O2`, but with Clang 14.0.0: https://godbolt.org/z/cTTbdrrvM

Start by reproducing the x86 -O2 crash with the provided C++ program and compare it with -disable-postra-machine-sink, other architectures, and Clang 14. Investigate the post-RA machine-sink pass and its x86-specific behavior. Done means the generated x86 binary no longer segfaults without disabling the pass, while the listed non-failing configurations remain valid.

Written by the indexing model from the issue text.