build failed on Linux with x32 ABI

[Maxim Dounin]

Hello!

On Wed, Jun 26, 2013 at 01:00:52PM +0300, Serguei I. Ivantsov wrote:

> Well, please apply the proper patch.
> It will also speeds up building on Linux, because rt signals (and
> included sysctl.h) are very rare nowadays.

I've committed slightly different version (with minor changes as 
requested by Igor), thanks.

-- 
Maxim Dounin
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