pagealign_alloc, vma-prot tests: Fix use of HAVE_MMAP (regr. yesterday). * m4/mmap-anon.m4 (gl_FUNC_MMAP_ANON): Test for sys/mman.h. Use ac_cv_header_sys_mman_h instead of gl_have_mmap. * lib/pagealign_alloc.c: Test HAVE_SYS_MMAN_H instead of HAVE_MMAP. * tests/test-vma-prot.c: Likewise.