Fix lldb-mi test data_read_memory_bytes_global

Summary:
Test was skipped because -data-evaluate-expression was thought
to not work on globals. This is not the case - the issue was clang
removes debug info for globals in cpp files that are not used.

Add a reference to the globals in question, and fix memory patter in
test to match memory pattern in testcase.

Reviewers: ki.stfu, abidh

Reviewed By: ki.stfu

Subscribers: aprantl, lldb-commits

Differential Revision: https://reviews.llvm.org/D37533

llvm-svn: 312726