Fix DebugInfo/prologue.swift for

llvm-project commit 1813652 removed the
prologue_end, so this test started failing. That directive is now
annotated with `is_stmt 0`.

Author: etcwilde

test/DebugInfo/prologue.swift

@@ -7,7 +7,7 @@ func markUsed<T>(_ t: T) {}
 // CHECK: .file [[F:[0-9]+]] "{{.*}}prologue.swift"
 func bar<T, U>(_ x: T, y: U) { markUsed("bar") }
 // CHECK: $s8prologue3bar_1yyx_q_tr0_lF:
-// CHECK: .loc	[[F]] 0 0 prologue_end
+// CHECK: .loc	[[F]] 0 0 is_stmt 0
 // Make sure there is no allocation happening between the end of
 // prologue and the beginning of the function body.
 // CHECK-NOT: callq	*