[lld] ELF: Add branch-to-branch optimization. (PR #138366)

[Fangrui Song via llvm-commits]

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@@ -93,6 +93,10 @@ Bind default visibility defined STB_GLOBAL function symbols locally for
 .Fl shared.
 .It Fl -be8
 Write a Big Endian ELF File using BE8 format(AArch32 only)
+.It Fl -branch-to-branch
+Enable the branch-to-branch optimizations: a branch whose target is
+another branch instruction is rewritten to point to the latter branch
+target (AArch64 and X86_64 only). Enabled by default at -O2.
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MaskRay wrote:

-O2 should use `.Fl O2.` (unfortunately the dot after `-O2` has to be highlighted as well...)

https://github.com/llvm/llvm-project/pull/138366