[llvm] [MC,ELF] Emit warning if a string constant contains newline char. (PR #98060)

[Fangrui Song via llvm-commits]

================
@@ -0,0 +1,50 @@
+// RUN: llvm-mc -filetype=obj -triple x86_64-pc-linux-gnu %s 2>&1 -o /dev/null | FileCheck -DFILE=%s --strict-whitespace %s --implicit-check-not=valid1_string --implicit-check-not=valid2_string --implicit-check-not=valid3_string --check-prefix=CHECK-WARN
----------------
MaskRay wrote:

Just use x86_64 as the triple to emphasize that the behavior is for all ELF (actually other object file formats as well, but we don't bother testing), not just Linux.

https://github.com/llvm/llvm-project/pull/98060