Introduce a limit on the depth of the template instantiation backtrace
we will print with each error that occurs during template
instantiation. When the backtrace is longer than that, we will print
N/2 of the innermost backtrace entries and N/2 of the outermost
backtrace entries, then skip the middle entries with a note such as:

  note: suppressed 2 template instantiation contexts; use
  -ftemplate-backtrace-limit=N to change the number of template
  instantiation entries shown

This should eliminate some excessively long backtraces that aren't
providing any value.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@101882 91177308-0d34-0410-b5e6-96231b3b80d8
12 files changed