[clang] [clang-repl] Fix PLT offset too large linker error on ARM (PR #78959)

[Stefan Gränitz via cfe-commits]

weliveindetail wrote:

The above patch landed after `release/18.x` branched. It drops the check for `CMAKE_SYSTEM_PROCESSOR` as discussed in this thread and only relies on the linker-flag check.

This seems to be the right thing to do. I checked on 32-bit Raspbian @ RPi4b: It correctly defaults to triple `arm-linux-gnueabihf`, but `CMAKE_SYSTEM_PROCESSOR` is `AARCH64`. Thus, on current `release/18.x` we skip adding the `--long-plt` flag in this case. (It doesn't have the resources to link clang-repl, but this is still incorrect.)

It might be a backporting candidate.

https://github.com/llvm/llvm-project/pull/78959