Add support for HYBRID_MALLOC, allowing the use of gmalloc before

Add support for HYBRID_MALLOC, allowing the use of gmalloc before
dumping and the system malloc after dumping.  (Bug#18222)

* configure.ac (HYBRID_MALLOC): New macro; define to use gmalloc
before dumping and the system malloc after dumping.  Define on Cygwin.
* src/conf_post.h (malloc, realloc, calloc, free) [HYBRID_MALLOC]:
Define as macros, expanding to hybrid_malloc, etc.
(HYBRID_GET_CURRENT_DIR_NAME): New macro.
(get_current_dir_name) [HYBRID_GET_CURRENT_DIR_NAME]: Define as
macro.
* src/gmalloc.c: Set up the infrastructure for HYBRID_MALLOC, with a
full implementation on Cygwin.  Remove Cygwin-specific code that
is no longer needed.
(malloc, realloc, calloc, free, aligned_alloc) [HYBRID_MALLOC]:
Redefine as macros expanding to gmalloc, grealloc, etc.
(DUMPED, ALLOCATED_BEFORE_DUMPING) [CYGWIN]: New macros.
(get_current_dir_name) [HYBRID_GET_CURRENT_DIR_NAME]: Undefine.
(USE_PTHREAD, posix_memalign) [HYBRID_MALLOC]: Don't define.
(hybrid_malloc, hybrid_calloc, hybrid_free, hybrid_realloc)
[HYBRID_MALLOC]:
(hybrid_get_current_dir_name) [HYBRID_GET_CURRENT_DIR_NAME]:
(hybrid_aligned_alloc) [HYBRID_MALLOC && (HAVE_ALIGNED_ALLOC ||
HAVE_POSIX_MEMALIGN)]: New functions.
* src/alloc.c (aligned_alloc) [HYBRID_MALLOC && (ALIGNED_ALLOC ||
HAVE_POSIX_MEMALIGN)]: Define as macro expanding to
hybrid_aligned_alloc; declare.
(USE_ALIGNED_ALLOC) [HYBRID_MALLOC && (ALIGNED_ALLOC ||
HAVE_POSIX_MEMALIGN)]: Define.
(refill_memory_reserve) [HYBRID_MALLOC]: Do nothing.
* src/sysdep.c (get_current_dir_name) [HYBRID_GET_CURRENT_DIR_NAME]:
Define as macro, expanding to gget_current_dir_name, and define
the latter.
* src/emacs.c (main) [HYBRID_MALLOC]: Don't call memory_warnings() or
malloc_enable_thread().  Don't initialize malloc.
* src/lisp.h (NONPOINTER_BITS) [CYGWIN]: Define (because GNU_MALLOC is
no longer defined on Cygwin).
(refill_memory_reserve) [HYBRID_MALLOC]: Don't declare.
* src/sheap.c (bss_sbrk_buffer_end): New variable.
* src/unexcw.c (__malloc_initialized): Remove variable.
* src/ralloc.c: Throughout, treat HYBRID_MALLOC the same as
SYSTEM_MALLOC.
* src/xdisp.c (decode_mode_spec) [HYBRID_MALLOC]: Don't check
	Vmemory_full.