[SystemZ] Add codegen test for global string alignment

This commit adds a test for the SystemZ backend that checks for the correct
alignment of global strings created by the PrintFOptimizer for the case
`printf("foo\n")` -> `puts("foo")`.

Author: dominik-steenken

llvm/test/Transforms/InstCombine/SystemZ/printf-opt-alignment.ll

@@ -0,0 +1,15 @@
+; RUN: opt < %s --passes=instcombine -S -mtriple=systemz-unknown | FileCheck %s
+;
+; Check that string replacements inserted by the instcombiner are properly aligned.
+; The specific case checked replaces `printf("foo\n")` with `puts("foo")`
+
+@msg1 = constant [17 x i8] c"Alignment Check\0A\00", align 2
+; CHECK: c"Alignment Check\00", align 2
+
+; Function Attrs: noinline nounwind
+define dso_local void @foo() #0 {
+  %call = call signext i32 (ptr, ...) @printf(ptr noundef @msg1)
+  ret void
+}
+
+declare signext i32 @printf(ptr noundef, ...) #1