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Issue 11214 reports problems with older versions of gdb.  It does work
with gdb 7.9 on my Ubuntu Trusty system, so take that as the minimum
required version.

Fixes #11214.

Change-Id: I61b732895506575be7af595f81fc1bcf696f58c2
Reviewed-on: https://go-review.googlesource.com/12626

Reviewed-by: Austin Clements <austin@google.com>