[debuginfo-tests] tweak new test to be compatible with wider range of compilers.

emplace_back was added in C++11, and its usage isn't critical to what's being
tested so using push_back instead will allow this test to work with more
compilers.

llvm-svn: 338371
GitOrigin-RevId: c5018d46f2da7671873457fef33a63c924b59175
1 file changed