* aclocal.m4 (AC_FUNC_MMAP_ANYWHERE): Completely rewritten.
Now defines HAVE_MMAP_DEV_ZERO and/or HAVE_MMAP_ANON depending
which you have.
(AC_FUNC_MMAP_FILE): Don't AC_REQUIRE AC_FUNC_MMAP_ANYWHERE.
* configure.in: Set GGC to ggc-page if any of mmap_dev_zero,
mmap_anon, and valloc is available.
* ggc-page.c: Restructure ifdef logic to match new autoconf
spec. Don't throw away the test page in init_ggc.