IRIX 6.5 (cc 7.4) needs -c99 to compile without whining.

Without -c99 including C99 header files like <stdint.h> is an error.

For gcc (used "freeware" 3.3), there just doesn't seem to be a way,
so claim there's no <stdint.h>.
Irix: the explicit <fcntl.h> is needed
Mention that freeware gdbm might be obsolete.