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

[James Henderson via llvm-commits]

================
@@ -0,0 +1,25 @@
+## Test for FileHeader Flags
+## When FLAGS variable isn't defined, the e_flags value is 0,
+## otherwise it's the specified value
----------------
jh7370 wrote:

Please don't resolve conversations that I started. I will resolve them when I'm happy you've addressed my request.

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