[SystemZ] Add codegen test for global string alignment

This commit adds a test to the `clang` test suite 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

clang/test/CodeGen/SystemZ/align-systemz-globalstring.c

@@ -0,0 +1,14 @@
+// RUN: %clang_cc1 -O1 -triple s390x-linux-gnu -emit-llvm %s -o - | FileCheck %s
+
+// #include <stdio.h>
+
+// CHECK: @msg1 = local_unnamed_addr constant [13 x i8] c"Hello World\0A\00", align 2
+// CHECK: @msg1.clipped = private unnamed_addr constant [12 x i8] c"Hello World\00", align 2
+
+const char msg1 [] = "Hello World\n";
+
+extern int printf(const char *__restrict __format, ...);
+
+void foo() {
+    printf(msg1);
+}