Testing 32-bit builds on Travis CI

[Rick Graham]

Total Travis noob here.

Wondering if any assignments in a Make.user, changes to Make.inc, changes to Makefile, and/or environment variable settings would force Travis to build Julia (and deps) using either the "-m32" or "-m32x" compiler switches.  If this is possible, it may trigger/show most of the 32/64-bit issues being reported.

Perhaps there are other Travis CI environment and/or build options that could be used so that automated testing of 32-bit systems is performed.