[CentOS] kernel mod compilation frustration

I want to add a sleep() to a module. It tells me it can't find <time.h>;
if I tell it "/usr/include/time.h", it gives me a ton of errors (I *have*
put the #include just above where I call sleep, not up at the top).

Any clues as to what I'm doing wrong? With kernel
/vmlinuz-2.6.18-194.3.1.el5, I just added the line
extern unsigned int sleep( unsigned int seconds );
and everything was wonderful; with the current kernel, it complains sleep
is undefined.

??
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