Implement debugging of WOW64 processes

Implement debugging of WOW64 processes

For WOW64 processes, the Wow64* variants of SuspendThread,
GetThreadContext, SetThreadContext, and GetThreadSelectorEntry have to
be used instead.
And instead of EnumProcessModules, EnumProcessModulesEx with
LIST_MODULES_32BIT is necessary.

gdb/ChangeLog:

2020-03-04  Hannes Domani  <ssbssa@yahoo.de>

	* NEWS: Mention support for WOW64 processes.
	* amd64-windows-nat.c (amd64_mappings): Rename and remove static.
	(amd64_windows_segment_register_p): Remove static.
	(_initialize_amd64_windows_nat): Update.
	* configure.nat <windows> (NATDEPFILES): Add i386-windows-nat.o.
	* i386-windows-nat.c (context_offset): Update.
	(i386_mappings): Rename and remove static.
	(i386_windows_segment_register_p): Remove static.
	(_initialize_i386_windows_nat): Update.
	* windows-nat.c (STATUS_WX86_BREAKPOINT): New macro.
	(STATUS_WX86_SINGLE_STEP): New macro.
	(EnumProcessModulesEx): New macro.
	(Wow64SuspendThread): New macro.
	(Wow64GetThreadContext): New macro.
	(Wow64SetThreadContext): New macro.
	(Wow64GetThreadSelectorEntry): New macro.
	(windows_set_context_register_offsets): Add static.
	(windows_set_segment_register_p): Likewise.
	(windows_add_thread): Adapt for WOW64 processes.
	(windows_fetch_one_register): Likewise.
	(windows_nat_target::fetch_registers): Likewise.
	(windows_store_one_register): Likewise.
	(display_selector): Likewise.
	(display_selectors): Likewise.
	(handle_exception): Likewise.
	(windows_continue): Likewise.
	(windows_nat_target::resume): Likewise.
	(windows_add_all_dlls): Likewise.
	(do_initial_windows_stuff): Likewise.
	(windows_nat_target::attach): Likewise.
	(windows_get_exec_module_filename): Likewise.
	(windows_nat_target::create_inferior): Likewise.
	(windows_xfer_siginfo): Likewise.
	(_initialize_loadable): Initialize Wow64SuspendThread,
	Wow64GetThreadContext, Wow64SetThreadContext,
	Wow64GetThreadSelectorEntry and EnumProcessModulesEx.
	* windows-nat.h (windows_set_context_register_offsets):
	Remove declaration.
	(windows_set_segment_register_p): Likewise.
	(i386_windows_segment_register_p): Add declaration.
	(amd64_windows_segment_register_p): Likewise.