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

[James Henderson via llvm-commits]

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@@ -0,0 +1,48 @@
+## 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:

```suggestion
## Test for FileHeader Flags; when FLAGS variable isn't defined, the e_flags value is 0, otherwise it's the specified value.
```
Please also split over multiple lines, to keep to the standard LLVM width of 80 characters.

Also, this is a test of yaml2obj behaviour, not obj2yaml. Please move the test to the test/tools/yaml2obj directory.

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