Enable TestDataFormatterStdIterator with GCC.

Summary:
This test now passes for Clang and GCC. I do not know why it was
disabled for GCC with link to a bug which should not have had an
effect on this test.

Test Plan: dotest.py -C gcc -p TestDataFormatterStdIterator

Reviewers: vharron

Subscribers: lldb-commits

Differential Revision: http://reviews.llvm.org/D8396

llvm-svn: 232552