Define ROUNDUP_PAGESIZE, ROUNDUP_GRANULE_SIZE macros (code refactoring)

Define ROUNDUP_PAGESIZE, ROUNDUP_GRANULE_SIZE macros (code refactoring)

* alloc.c (GC_expand_hp_inner): Use ROUNDUP_PAGESIZE().
* checksums.c (GC_record_fault, GC_was_faulted): Likewise.
* os_dep.c (GC_unix_mmap_get_mem, GC_wince_get_mem, GC_unmap_start,
GC_remove_protection): Likewise.
* headers.c (GC_scratch_alloc): Use ROUNDUP_GRANULE_SIZE().
* malloc.c (GC_alloc_large): Likewise.
* mallocx.c (GC_malloc_many): Likewise.
* headers.c (GC_scratch_alloc): Use ROUNDUP_PAGESIZE() (only if
USE_MMAP).
* include/private/gc_priv.h (ROUNDUP_GRANULE_SIZE, ROUNDUP_PAGESIZE):
Define macro to round up a value to a multiple of a granule or a page,
respectively.