[llvm] [NFC] Add SHF_NONE to fix Werror=extra warning (PR #112808)

[Matt Arsenault via llvm-commits]

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@@ -1180,6 +1180,9 @@ enum : unsigned {
 
 // Section flags.
 enum : unsigned {
+  // No flag
+  SHF_NONE = 0x0,
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arsenm wrote:

Does the standard define this value? Maybe should avoid introducing names that aren't used in it 

https://github.com/llvm/llvm-project/pull/112808