generalize ELF hash table types not to assume 32-bit entries

alpha and s390x gratuitously use 64-bit entries (wasting 2x space and
cache utilization) despite the values always being 32-bit.

based on patch by Bobby Bingham, with changes suggested by Alexander
Monakov to use the public Elf_Symndx type from link.h (and make it
properly variable by arch) rather than adding new internal
infrastructure for handling the type.

include/link.h

@@ -16,8 +16,7 @@ extern "C" {
 #define ElfW(type) Elf32_ ## type
 #endif
 
-/* this is the same everywhere except alpha and s390 */
-typedef uint32_t Elf_Symndx;
+#include <bits/link.h>
 
 struct dl_phdr_info {
 	ElfW(Addr) dlpi_addr;