X86 entry code related updates: - Consolidate the macros for .byte ... opcode sequences - Deduplicate register offset defines in include files - Simplify the ia32,x32 compat handling of the related syscall tables to get rid of #ifdeffery. - Clear all EFLAGS which are not required for syscall handling - Consolidate the syscall tables and switch the generation over to the generic shell script and remove the CFLAGS tweaks which are not longer required. - Use 'int' type for system call numbers to match the generic code. - Add more selftests for syscalls