Fixes warnings on 32-bit (x86).

1. Cast sizeof() to match printf specifier
2. Cast off_t to long long.  This is guaranteed 64-bit.
   No performance concern because it's an error message.

attic/_hashindex.c: In function ‘hashindex_read’:
attic/_hashindex.c:148:13: warning: format ‘%ld’ expects argument of type ‘long
int’, but argument 4 has type ‘unsigned int’ [-Wformat=]
             EPRINTF_MSG_PATH(path, "failed to read %ld bytes", sizeof(HashHeader));
             ^
attic/_hashindex.c:188:13: warning: format ‘%ld’ expects argument of type ‘long
int’, but argument 4 has type ‘off_t’ [-Wformat=]
             EPRINTF_MSG_PATH(path, "failed to read %ld bytes", length);
             ^