Fix '~' operator application to unsigned values shorter than word

Fix '~' operator application to unsigned values shorter than word

Without the fix, unsigned result of "~" operator is zero-extended
to a wide type (word) thus the result has leading zeros (which is
not expected to be).

* dyn_load.c [HAVE_DL_ITERATE_PHDR] (GC_register_dynlib_callback):
Cast (sizeof(word)-1) to word before "~" operation.
* mark.c (GC_mark_from): Likewise.
* mark_rts.c (GC_add_roots_inner, GC_exclude_static_roots): Likewise.
* mark_rts.c [!MSWIN32 && !MSWINCE && !CYGWIN32]
(GC_remove_roots_inner): Likewise.
* os_dep.c [SVR4 || AUX || DGUX || LINUX && SPARC]
(GC_SysVGetDataStart): Likewise.
* os_dep.c [!MSWIN32 && DATASTART_USES_BSDGETDATASTART]
(GC_FreeBSDGetDataStart): Likewise.
* dyn_load.c [(MSWIN32 || MSWINCE || CYGWIN32) && !GC_WIN32_THREADS]
(GC_cond_add_roots): Cast (dwAllocationGranularity-1) to word before
"~" operation.
* include/private/gc_priv.h (HBLKPTR): Cast (HBLKSIZE-1) to word
before "~" operation.
* os_dep.c [USE_WINALLOC || CYGWIN32] (GC_win32_get_mem): Likewise.
* mark.c (GC_mark_from): Change type of new_size local variable from
int to word.
* os_dep.c [OPENBSD] (GC_find_limit_openbsd, GC_skip_hole_openbsd):
Change type of pgsz local variable from size_t to word (to avoid
implicit unsigned value extension after "~" operation).
* os_dep.c [PROC_VDB] (GC_read_dirty): Cast (sizeof(long)-1) to word
before "~" operation.