[V2 PATCH 0/5] Handle first hidden parameter

[Yao Qi <yao at codesourcery dot com>]

Hi,
This patch series is the version 2, and version 1 can be found here,

  [PATCH 1/4] New gdb arch hook: return_with_first_hidden_param_p
  http://sourceware.org/ml/gdb-patches/2012-04/msg00565.html

The version 1 was approved by Tom, but Mark K. thinks "first hidden
parameter" is special in language c++ on some arch, instead of
all languages.

  http://sourceware.org/ml/gdb-patches/2012-05/msg00671.html

I re-design this patch a little bit.  In version 2, the "first
hidden parameter" is treated as a special feature of a combination
of a certain language and a certain arch.  I add new language
hook 'la_return_by_reference', which is equal to
'la_pass_by_reference' in default, and I overwrite the default
in language c++ to honour gdbarch_return_in_first_hidden_param.
In this way, we can reduce the impact of this change on a certain
arch in c++ only.

Compared with v1, there are some changes,

  - new language hook la_return_by_reference.
  - rename gdbarch hook to return_in_first_hidden_param, and remove
TYPE parameter of it.

patch 3/5 ~ 5/5 is unchanged, compared with v1.