[TestMiVar] Enable one of the tests for GCC.

Summary:
The "internal" name of vars is different between clang and GCC. All this
change does is to use a regex instead of the hardcoded internal name.

Test Plan: dotest.py -C <clang|gcc> -p TestMiVar

Reviewers: ki.stfu

Reviewed By: ki.stfu

Subscribers: lldb-commits

Differential Revision: http://reviews.llvm.org/D9128

llvm-svn: 236024