* system.h: Consolidate ENABLE_VALGRIND_CHECKING-dependent defines
	here.
	[!VALGRIND_MAKE_MEM_NOACCESS]: Define as VALGRIND_MAKE_NOACCESS.
	[!VALGRIND_MAKE_MEM_DEFINED]: Define as VALGRIND_MAKE_READABLE.
	[!VALGRIND_MAKE_MEM_UNDEFINED]: Define as VALGRIND_MAKE_WRITABLE.
	* ggc-common.c: Remove ENABLE_VALGRIND_CHECKING-dependent defines.
	Replace use of VALGRIND_MAKE_READABLE, VALGRIND_MAKE_WRITABLE, and
	VALGRIND_MAKE_NOACCESS with VALGRIND_MAKE_MEM_DEFINED,
	VALGRIND_MAKE_MEM_UNDEFINED, and VALGRIND_MAKE_MEM_NOACCESS
	respectively.
	* ggc-zone.c: Similar.
	* ggc-page.c: Similar.

From-SVN: r132407