[lld] [LLD][AArch64] Mark .plt with PURECODE flag if all input sections also have it (PR #132224)

[Csanád Hajdú via llvm-commits]

Il-Capitano wrote:

I opened https://github.com/llvm/llvm-project/pull/132412 as a general approach of dealing with a mix of XO and RX sections in the same binary. I'll close this PR because of that. I'll do a separate change regarding the section flags for `.plt` and `.iplt`.

https://github.com/llvm/llvm-project/pull/132224