elang/compiler: Get rid of an unused include directive from "analyze/namespace_analyzer.h".
elang/compiler: Check invalid compilation unit.
elang/compiler: Introduce |TestDriver::GetBaseClasses()| and utilzie it.
elang/compiler/testing: Introduce |CompilerTest| base class for compiler testing.
elang/compiler/synatx: Utilize |testing::CompilerTest| for parser testing.
elang/compiler: Make |ast::Alias::BintTo()| not to accept |ast::Alias| as target.
elang/compiler/analyze: Add "NamespaceAnalyzerTest.AliasToAliasDeep" test.