[lldb] Fix a warning

This patch fixes:

  third-party/unittest/googletest/include/gtest/gtest.h:1379:11:
  error: comparison of integers of different signs: 'const int' and
  'const unsigned long' [-Werror,-Wsign-compare]

Author: kazutakahirata

lldb/unittests/Core/TelemetryTest.cpp

@@ -87,7 +87,7 @@ TEST(TelemetryTest, PluginTest) {
   entry.msg = "";
 
   ASSERT_THAT_ERROR(ins->dispatch(&entry), ::llvm::Succeeded());
-  ASSERT_EQ(1, expected_entries.size());
+  ASSERT_EQ(1U, expected_entries.size());
   EXPECT_EQ("In FakePlugin",
             llvm::dyn_cast<lldb_private::FakeTelemetryInfo>(expected_entries[0])
                 ->msg);