Clean up compiler warnings from { gcc -Wall }, many of which I introduced with

the ClamAV and openssl_options patches in this release.

Logic in buildconfig.c for adjusting some print format strings assumed that
long ints were four bytes; adjust to test this against reality, to remove
spurious warnings on my dev box (FreeBSD/amd64).

Note: this commit adds a buildconfig.h dependency upon inttypes.h, which was in
SUSv2, so should be safe.