pull gdb 7.6.1 from upstream to master

BUG=None
TEST=None

Change-Id: I17b7f2b056e2cbd841081d1778b9526eddf714bf
Reviewed-on: https://chromium-review.googlesource.com/171378
Reviewed-by: Luis Lozano <llozano@chromium.org>
Commit-Queue: Yunlian Jiang <yunlian@chromium.org>
Tested-by: Yunlian Jiang <yunlian@chromium.org>
5204 files changed