[lld] [LLD][ELF][AArch64] Add BTI Aware long branch thunks (PR #108989)

[Fangrui Song via llvm-commits]

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+// REQUIRES: aarch64
+// RUN: rm -rf %t && split-file %s %t && cd %t
+// RUN: llvm-mc -filetype=obj -triple=aarch64 asm -o %t.o
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MaskRay wrote:

After `rm -rf %t && split-file %s %t && cd %t`, `%t` can be completely avoided.
For example, name an output file `a.o` and output as `out` instead `%t.exe`

https://github.com/llvm/llvm-project/pull/108989