[clang-diff] Refactor stop-after command-line flag

Summary:
Rename stop-after to stop-diff-after. When building LLVM with
-DLLVM_BUILD_LLVM_DYLIB=ON, stop-after collides with the stop-after
already present in LLVM.

Reviewers: johannes, arphaman

Subscribers: klimek, aheejin, cfe-commits

Differential Revision: https://reviews.llvm.org/D36989

llvm-svn: 311476
diff --git a/clang/test/Tooling/clang-diff-topdown.cpp b/clang/test/Tooling/clang-diff-topdown.cpp
index 8e78a03..d6c1d77 100644
--- a/clang/test/Tooling/clang-diff-topdown.cpp
+++ b/clang/test/Tooling/clang-diff-topdown.cpp
@@ -1,6 +1,6 @@
 // RUN: %clang_cc1 -E %s > %t.src.cpp
 // RUN: %clang_cc1 -E %s > %t.dst.cpp -DDEST
-// RUN: clang-diff -dump-matches -stop-after=topdown %t.src.cpp %t.dst.cpp -- -std=c++11 | FileCheck %s
+// RUN: clang-diff -dump-matches -stop-diff-after=topdown %t.src.cpp %t.dst.cpp -- -std=c++11 | FileCheck %s
 //
 // Test the top-down matching of identical subtrees only.