release_33 branch: proposing r183297

[Dimitry Andric]

Hi,

For the 3.3 release branch, I would like to propose merging r183297:

r183297 from llvm trunk (by David Blaikie):

  PR15662: Optimized debug info produces out of order function
  parameters

  When a function is inlined we lazily construct the variables
  representing the function's parameters. After that, we add any
  remaining unused parameters.

  If the function doesn't use all the parameters, or uses them out of
  order, then the DWARF would produce them in that order, producing a
  parameter order that doesn't match the source.

  This fix causes us to always keep the arg variables at the start of
  the variable list & in the original order from the source.

On FreeBSD, this enables DTrace to work properly on certain functions compiled with optimization, where previously the debug information had its arguments swapped around.

This commit should apply to the release_33 branch without modification.

-Dimitry