[ghost] Kernel now parses the \ghost keyword

src/kernel_internals/parsing/clexer.mll

src/kernel_internals/parsing/cparser.mly

src/kernel_internals/typing/cabs2cil.ml

src/kernel_services/ast_printing/cabs_debug.ml

src/kernel_services/ast_printing/cil_printer.ml

src/kernel_services/ast_printing/cprint.ml

src/kernel_services/parsetree/cabs.ml

tests/syntax/oracle/ghost_cv_parsing_errors.0.res.oracle

tests/syntax/oracle/ghost_cv_parsing_errors.1.res.oracle

tests/syntax/oracle/ghost_cv_parsing_errors.2.res.oracle