checking changes for warning regressions

[Roland McGrath]

> If it is true, why can't we use uint64_t for bswap_64?

We can if we think it's OK for all the headers using <bits/byteswap.h>
to include <stdint.h> and put all those symbols into the name space.
That may well be fine, but it needs careful consideration.

The conservative change is to conditionalize the use of long vs long long
in bits/byteswap.h--that just fixes the regression, without changing the
API of any public header.


Thanks,
Roland