Include alloca.h unconditionally

Include alloca.h unconditionally

Since gnulib alloca module was imported, we can include alloca.h in
both gdb and gdbserver unconditionally, so this patch adds inclusion
of alloca.h in common-defs.h.  This patch also removes AC_FUNC_ALLOCA
in configure.ac because we don't need to check alloca any more.

This patch below is removed in fact.

  [RFA/commit] include alloca.h if available.
  https://www.sourceware.org/ml/gdb-patches/2010-08/msg00566.html

Since alloca.h is from gnulib now, we don't have to check malloc.h in
configure and include malloc.h in code.  This patch also remove them
too.

gdb:

2014-11-21  Yao Qi  <yao@codesourcery.com>

	* common/common-defs.h: Include alloca.h
	* configure.ac: Don't invoke AC_FUNC_ALLOCA.
	* configure: Re-generated.
	* defs.h: Remove code handling alloca.
	* utils.c (gdb_realpath): Don't check HAVE_ALLOCA is defined
	or not.

gdb/gdbserver:

2014-11-21  Yao Qi  <yao@codesourcery.com>

	* configure.ac: Don't invoke AC_FUNC_ALLOCA.
	(AC_CHECK_HEADERS): Remove malloc.h.
	* configure: Re-generated.
	* config.in: Re-generated.
	* server.h: Don't include alloca.h and malloc.h.
	* gdbreplay.c: Don't check HAVE_ALLOCA_H is defined.
	Don't include malloc.h.