Sporadic CI failures in std.process (x86)

[David Nadlinger]

The Travis CI tests for std.process on Linux x86 have started to fail 
sporadically, see e.g. 
https://travis-ci.org/ldc-developers/ldc/jobs/11404239 and some of the 
builds before that.

It seems to be an OOM problem on the CI slave, but it's something we 
should investigate at some point anyway as it renders the build status 
indicator unreliable.

David