configure.in: Look for <valgrind/memcheck.h> first.

configure.in: Look for <valgrind/memcheck.h> first.

	* configure.in <enable-checking for valgrind>: Look for
	<valgrind/memcheck.h> first.  AC_DEFINE HAVE_VALGRIND_MEMCHECK_H
	if it exists.
	* configure, config.in: Regenerate.
	* ggc-common.c [ENABLE_VALGRIND_CHECKING &&
	HAVE_VALGRIND_MEMCHECK_H]: Include <valgrind/memcheck.h>.  Use
	#elif for other alternatives.
	* ggc-page.c: Ditto.
	* ggc-zone.c: Don't assume <valgrind/memcheck.h>; instead copy
	include structure from ggc-common.c.

From-SVN: r73065