[llvm] [SystemZ] Add proper mcount handling (PR #135767)

[Ulrich Weigand via llvm-commits]

================
@@ -558,6 +559,32 @@ void SystemZELFFrameLowering::emitPrologue(MachineFunction &MF,
   // to determine the end of the prologue.
   DebugLoc DL;
 
+  // Add mcount instrumentation if necessary.
+  if (MF.getFunction().getFnAttribute("systemz-backend").getValueAsString() ==
+      "insert-mcount") {
----------------
uweigand wrote:

I'd prefer a more specific attribute name, like "systemz-instrument-function-entry", where the value is the actual mcount function name - similar to the common attribute.

https://github.com/llvm/llvm-project/pull/135767