Relax the constraints on a debuginfo test

The snapshot just failed due to a debuginfo test failing, and according to its
output at
http://buildbot.rust-lang.org/builders/snap3-linux/builds/564/steps/test/logs/stdio
it appears to be because the printed lines has a little less information than
the original lines were checking for. I would suspect that this is just because
of a slightly different version of gdb, but it's not that serious regardless.
auto merge of #10276 : alexcrichton/rust/fix-debug-info, r=jdm

The snapshot just failed due to a debuginfo test failing, and according to its
output at
http://buildbot.rust-lang.org/builders/snap3-linux/builds/564/steps/test/logs/stdio
it appears to be because the printed lines has a little less information than
the original lines were checking for. I would suspect that this is just because
of a slightly different version of gdb, but it's not that serious regardless.