[clang] Add unreachable after fully covered switches, avoid GCC warnings. NFC. (#159330)

This avoids the following warnings:

    ../../clang/lib/AST/ExprConstant.cpp: In member function ‘bool {anonymous}::IntExprEvaluator::VisitBuiltinCallExpr(const clang::CallExpr*, unsigned int)’:
    ../../clang/lib/AST/ExprConstant.cpp:14104:3: warning: this statement may fall through [-Wimplicit-fallthrough=]
    14104 |   }
          |   ^
    ../../clang/lib/AST/ExprConstant.cpp:14105:3: note: here
    14105 |   case Builtin::BIstrlen:
          |   ^~~~
    ../../clang/lib/Driver/ToolChains/CommonArgs.cpp: In function ‘std::string clang::driver::tools::complexRangeKindToStr(clang::LangOptionsBase::ComplexRangeKind ’:
    ../../clang/lib/Driver/ToolChains/CommonArgs.cpp:3523:1: warning: control reaches end of non-void function [-Wreturn-type]
     3523 | }
          | ^

0 files changed, 0 insertions, 0 deletions