[lld] [ELF] Add support for PT_OPENBSD_NOBTCFI (PR #120005)

[Brad Smith via llvm-commits]

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@@ -1487,6 +1487,7 @@ static void readConfigs(Ctx &ctx, opt::InputArgList &args) {
       args, "keep-text-section-prefix", "nokeep-text-section-prefix", false);
   ctx.arg.zLrodataAfterBss =
       getZFlag(args, "lrodata-after-bss", "nolrodata-after-bss", false);
+  ctx.arg.zNoBtCfi = hasZOption(args, "nobtcfi");
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brad0 wrote:

Also the comment at the top of setConfigs() doesn't really align with this being added there..
```
// Some Config members do not directly correspond to any particular
// command line options, but computed based on other Config values.
```

https://github.com/llvm/llvm-project/pull/120005