[libc] [UnitTest] Give UnitTest gtest like colors

[abrachet]

Summary

This is a quality of life change to make it a little nicer to look at, NFC.
This patch makes the RUN and OK lines green and FAILED lines red to match gtest's output.

[abrachet]

Ran clang-format

[sivachandra]

Thanks for this!

libc/utils/UnitTest/Test.cpp

void Test::addTest(Test *T) {
   End = T;
 }
 
 int Test::runTests() {
   int TestCount = 0;
   int FailCount = 0;
   for (Test *T = Start; T != nullptr; T = T->Next, ++TestCount) {
     const char *TestName = T->getName();
-    llvm::outs() << "[ RUN      ] " << TestName << '\n';
+    constexpr auto GREEN = llvm::raw_ostream::GREEN;
+    constexpr auto RED = llvm::raw_ostream::RED;
+    constexpr auto RESET = llvm::raw_ostream::RESET;
+    llvm::outs() << GREEN << "[ RUN      ] " << RESET << TestName << '\n';
     RunContext Ctx;
     T->SetUp();
     T->Run(Ctx);
     T->TearDown();
     auto Result = Ctx.status();
     switch (Result) {
     case RunContext::Result_Fail:
-      llvm::outs() << "[  FAILED  ] " << TestName << '\n';
+      llvm::outs() << RED << "[  FAILED  ] " << RESET << TestName << '\n';
       ++FailCount;
       break;
     case RunContext::Result_Pass:
-      llvm::outs() << "[       OK ] " << TestName << '\n';
+      llvm::outs() << GREEN << "[       OK ] " << RESET << TestName << '\n';
       break;
     }
   }
 
   llvm::outs() << "Ran " << TestCount << " tests. "
                << " PASS: " << TestCount - FailCount << ' '
                << " FAIL: " << FailCount << '\n';