On Windows, starting a new process with GDBserver seems to work,
in the sense that the program does get started, and GDBserver
confirms that it is listening for GDB to connect. However, as soon as
GDB establishes the connection with GDBserver, and starts discussing
with it, GDBserver crashes, with a SEGV.

This SEGV occurs in remote-utils.c::prepare_resume_reply...

  | regp = current_target_desc ()->expedite_regs;
  | [...]
  | while (*regp)

... because, in our case, REGP is NULL.

This patches fixes the issues by adding a parameter to init_target_desc,
in order to make sure that we always provide the list of registers when
we initialize a target description.

gdb/ChangeLog:

        PR server/23158:
        * regformats/regdat.sh: Adjust script, following the addition
        of the new expedite_regs parameter to init_target_desc.

gdb/gdbserver/ChangeLog:

        PR server/23158:
        * tdesc.h (init_target_desc) <expedite_regs>: New parameter.
        * tdesc.c (init_target_desc) <expedite_regs>: New parameter.
        Use it to set the expedite_regs field in the given tdesc.
        * x86-tdesc.h: New file.
        * linux-aarch64-tdesc.c (aarch64_linux_read_description):
        Adjust following the addition of the new expedite_regs parameter
        to init_target_desc.
        * linux-tic6x-low.c (tic6x_read_description): Likewise.
        * linux-x86-tdesc.c: #include "x86-tdesc.h".
        (i386_linux_read_description, amd64_linux_read_description):
        Adjust following the addition of the new expedite_regs parameter
        to init_target_desc.
        * lynx-i386-low.c: #include "x86-tdesc.h".
        (lynx_i386_arch_setup): Adjust following the addition of the new
        expedite_regs parameter to init_target_desc.
        * nto-x86-low.c: #include "x86-tdesc.h".
        (nto_x86_arch_setup): Adjust following the addition of the new
        expedite_regs parameter to init_target_desc.
        * win32-i386-low.c: #include "x86-tdesc.h".
        (i386_arch_setup): Adjust following the addition of the new
        expedite_regs parameter to init_target_desc.