Support/PathV2: Add replace_extension implementation.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@120514 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/unittests/Support/Path.cpp b/unittests/Support/Path.cpp
index 5ab74e1..823b078 100644
--- a/unittests/Support/Path.cpp
+++ b/unittests/Support/Path.cpp
@@ -103,6 +103,10 @@
     if (error_code ec = sys::path::remove_filename(temp_store))
       ASSERT_FALSE(ec.message().c_str());
     outs() << "    remove_filename: " << temp_store << '\n';
+    temp_store = *i;
+    if (error_code ec = sys::path::replace_extension(temp_store, "ext"))
+      ASSERT_FALSE(ec.message().c_str());
+    outs() << "    replace_extension: " << temp_store << '\n';
 
     outs().flush();
   }