[llvm] Allow "[[FLAGS=<none>]]" value in the ELF Fileheader Flags field (PR #143845)

[James Henderson via llvm-commits]

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@@ -0,0 +1,24 @@
+## Test for FileHeader Flags
+## When FLAGS variable isn't defined, the e_flags value is 0,
+## Otherwise it's the specified value
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jh7370 wrote:

You missed my other requests.
```suggestion
## Test for FileHeader Flags.
## When FLAGS variable isn't defined, the e_flags value is 0.
## Otherwise, it's the specified value
```

https://github.com/llvm/llvm-project/pull/143845