[llvm] [lit] Are all RUN lines skipped in windows cmd? (PR #65242)

[Martin Storsjö via llvm-commits]

mstorsjo wrote:

FWIW, this PR doesn't entirely fix running the tests with win32 cmd.exe either; with this PR, it fails like this:
```
Exit Code: 255

Command Output (stdout):
--

C:\code\llvm-project\llvm\build\test\MC\AArch64>echo 'RUN: at line 3' > nul &&

--
Command Output (stderr):
--
The syntax of the command is incorrect.

```

https://github.com/llvm/llvm-project/pull/65242