[lld] [lld] Add target support for SystemZ (s390x) (PR #75643)

[Fangrui Song via llvm-commits]

================
@@ -0,0 +1,72 @@
+// REQUIRES: systemz
----------------
MaskRay wrote:

Nit: just use `# ` for all new assembly tests

`systemz-ifunc-nonpreemptible.s` is a better name. See riscv-ifunc-nonpreemptible.s to test `--apply-dynamic-relocs`

https://github.com/llvm/llvm-project/pull/75643