bug#18702: libsodium fails to build on i686

[Mark H Weaver]

Hydra has never successfully built libsodium on i686, though it succeeds
on both x86_64 and mips64el.  See:

  http://hydra.gnu.org/job/gnu/master/libsodium-1.0.0.i686-linux
  http://hydra.gnu.org/job/gnu/master/libsodium-0.5.0.i686-linux

The configure script apparently hangs here:

--8<---------------cut here---------------start------------->8---
checking if gcc -std=gnu99 supports -fno-rtti -fno-exceptions... no
checking for gcc -std=gnu99 option to produce PIC... -fPIC -DPIC
checking if gcc -std=gnu99 PIC flag -fPIC -DPIC works... yes
checking if gcc -std=gnu99 static flag -static works... building of 
`/gnu/store/61lwfp7mk1da0kip76i1kn4gxf0mfp4n-libsodium-1.0.0.drv' timed out 
after 3600 seconds of silence
@ build-failed /gnu/store/61lwfp7mk1da0kip76i1kn4gxf0mfp4n-libsodium-1.0.0.drv 
- timeout
--8<---------------cut here---------------end--------------->8---

       Mark