Update slang for LLVM merge up to r187914.

Move OptParser.td dependency to use LLVM's version.
Switch to llvm::sys::fs::F_* enums.
Switch to LLVM Option handling library (not in Clang any more).
Add new ALIASARGS field to OPTION macro.
Switch to clang::getLastArgIntValue() helper function.
Use llvm::sys::fs::OpenFlags as enum and not unsigned int.
Remove unused DisableSimplifyLibCalls().
Switch to llvm::sys::fs::create_directories().

Change-Id: I9b12e18b759536c762ea0dd43356907ee53dbddb
7 files changed