[Kernel] remove __thread_is_keyword from machdep

Makefile.generating

config.h.in

configure.in

doc/developer/advance.tex

share/Makefile.config.in

share/machdep.c

src/kernel_internals/runtime/machdeps.ml

src/kernel_services/ast_data/cil_types.mli

src/kernel_services/ast_printing/cil_types_debug.ml

src/kernel_services/ast_queries/file.ml

tests/misc/custom_machdep/custom_machdep.ml

tests/misc/oracle/print_machdep.res.oracle

tests/syntax/machdep_char_unsigned.ml