Add "-gmodules" support to the test suite.

This change adds the capability of building test inferiors
with the -gmodules flag to enable module debug info support.
Windows is excluded per @zturner.

Reviewers: granata.enrico, aprantl, zturner, labath

Subscribers: zturner, labath, lldb-commits

Differential Revision: http://reviews.llvm.org/D19998

llvm-svn: 270848