Simplify data_start configuration.

Simplify data_start configuration.

This is a followon simplification to the fix for Bug#13650.
* admin/CPP-DEFINES (DATA_START, ORDINARY_LINK): Remove.
* configure.ac (CRT_DIR, LIB_STANDARD, START_FILES, DATA_START)
(LD_FIRSTFLAG, ORDINARY_LINK, LIB_GCC): Remove.
(AC_CHECK_HEADERS_ONCE): Remove sys/resource.h, as it's
not always needed.
(HAVE_DATA_START): New macro.
* etc/PROBLEMS (LIBS_SYSTEM, LIBS_MACHINE, LIBS_STANDARD): Remove.
Remove legacy-systems section, as this stuff is no longer
applicable with current linking strategies.
* src/Makefile.in (LD_FIRSTFLAG, LIB_GCC, CRT_DIR, LIB_STANDARD)
(START_FILES): Remove.  All uses removed.
(otherobj): Remove $(VMLIMIT_OBJ), as it's now first.
(ALLOBJS): Move here from autodeps.mk, and with VMLIMITS_OBJ first.
(buildobj.h): Use it.
($(ALLOBJS)): Depend on globals.h.
(temacs$(EXEEXT)): Use $(ALLOBJS).
* src/autodeps.mk (ALLOBJS): Move to Makefile.in.
* src/deps.mk (vm-limit.o):
* src/makefile.w32-in ($(BLD)/vm-limit.$(O)):
Do not depend on mem-limits.h.
* src/emacs.c (__do_global_ctors, __do_global_ctors_aux)
(__do_global_dtors, __CTOR_LIST__, __DTOR_LIST__)
[__GNUC__ && !ORDINARY_LINK]: Remove.
* src/mem-limits.h, src/pre-crt0.c: Remove.
* src/unexaix.c, src/unexcoff.c: Don't include mem-limits.h.
* src/unexcoff.c (etext): New decl.
(make_hdr): Use it instead of start_of_data.
* src/vm-limit.c: Move most of mem-limits.h's contents here.
(data_start): New decl.  It's OK if this is approximate,
so simplify-away some unnecessary exactness.
(POINTER): Remove; all uses removed.
(data_space_start): Now char *, to avoid casts.
(exceeds_lisp_ptr): New function, replacing the old
EXCEEDS_LISP_PTR macro.  All uses changed.
(check_memory_limits): Simplify and remove casts.
(start_of_data) [!CANNOT_DUMP || !SYSTEM_MALLOC]: Remove.
(memory_warnings): Use data_start instead of start_of_data.

Fixes: debbugs:13783