Fix signed/unsigned comparison warning in a unit test. This was appearing on
lld-x86_64-darwin13.

llvm-svn: 299749
diff --git a/lld/unittests/CoreTests/ParallelTest.cpp b/lld/unittests/CoreTests/ParallelTest.cpp
index f02db92..bd85070 100644
--- a/lld/unittests/CoreTests/ParallelTest.cpp
+++ b/lld/unittests/CoreTests/ParallelTest.cpp
@@ -42,5 +42,5 @@
   std::fill(expected, expected + 2049, 2);
   ASSERT_TRUE(std::equal(range, range + 2049, expected));
   // Check that we don't write past the end of the requested range.
-  ASSERT_EQ(range[2049], 1);
+  ASSERT_EQ(range[2049], 1u);
 }