Reapply r160148 (reverted in r163570) fixing spurious breakpoints in modern GDB

This reapplies the fix for PR13303 now with more justification. Based on my
execution of the GDB 7.5 test suite this results in:

expected passes: 16101 -> 20890 (+30%)
unexpected failures: 4826 -> 637 (-77%)

There are 23 checks that used to pass and now fail. They are all in
gdb.reverse. Investigating a few looks like they were accidentally passing
due to extra breakpoints being set by this bug. They're generally due to the
difference in end location between gcc and clang, the test suite is trying to
set breakpoints on the closing '}' that clang doesn't associate with any
instructions.

llvm-svn: 169304