Fix (adjust) GC_scratch_alloc actual argument type
* dyn_load.c [IRIX5 || USE_PROC_FOR_LIBRARIES && !LINUX]
(GC_register_dynamic_libraries): Do not cast GC_scratch_alloc argument
to word type (it should be of size_t).
* headers.c (alloc_hdr, GC_init_headers, get_index): Likewise.
* os_dep.c [PROC_VDB] (GC_proc_buf_size): Change type from word to size_t.
* os_dep.c [PROC_VDB] (GC_read_dirty): Change type of new_size local
variable (which is passed to GC_scratch_alloc) from word to size_t.