[llvm] MIPS/Asm/O32: Don't add another $ to PrivateGlobal symbol (PR #80644)

[Fangrui Song via llvm-commits]

MaskRay wrote:

Suggested description:

When parsing the `la` macro, we add a duplicate `$` prefix in `getOrCreateSymbol`,
leading to `error: Undefined temporary symbol $$yy` for code like:

```
xx:
	la	$2,$yy
$yy:
	nop
```

Remove the duplicate prefix.

In addition, recognize `.L`-prefixed symbols as local for O32.

https://github.com/llvm/llvm-project/pull/80644