Declare abstract class ArgumentsAdjuster. This abstract interface describes

a command line argument adjuster, which is responsible for command line
arguments modification before the arguments are used to run a frontend action.

Define class ClangSyntaxOnlyAdjuster implements ArgumentsAdjuster interface.
This class converts input command line arguments to the "syntax check only"
variant.

Reviewed by Manuel Klimek.

llvm-svn: 156478