/usr/include/clang/Lex/ is in libclang-dev 3.0-6ubuntu3.
This file is owned by root:root, with mode 0o755.
..
/usr/include/clang/Lex/AttrSpellings.inc
/usr/include/clang/Lex/CodeCompletionHandler.h
/usr/include/clang/Lex/DirectoryLookup.h
/usr/include/clang/Lex/ExternalPreprocessorSource.h
/usr/include/clang/Lex/HeaderMap.h
/usr/include/clang/Lex/HeaderSearch.h
/usr/include/clang/Lex/LexDiagnostic.h
/usr/include/clang/Lex/Lexer.h
/usr/include/clang/Lex/LiteralSupport.h
/usr/include/clang/Lex/MacroInfo.h
/usr/include/clang/Lex/ModuleLoader.h
/usr/include/clang/Lex/MultipleIncludeOpt.h
/usr/include/clang/Lex/PPCallbacks.h
/usr/include/clang/Lex/PTHLexer.h
/usr/include/clang/Lex/PTHManager.h
/usr/include/clang/Lex/Pragma.h
/usr/include/clang/Lex/PreprocessingRecord.h
/usr/include/clang/Lex/Preprocessor.h
/usr/include/clang/Lex/PreprocessorLexer.h
/usr/include/clang/Lex/ScratchBuffer.h
/usr/include/clang/Lex/Token.h
/usr/include/clang/Lex/TokenConcatenation.h
/usr/include/clang/Lex/TokenLexer.h