[v3] fix autoconf examples for testing C++11 support

[Jonathan Wakely]

On 6 November 2011 23:25, Jonathan Wakely wrote:
> The autoconf examples at
> http://gcc.gnu.org/onlinedocs/libstdc++/manual/backwards.html#id541888
> are incorrect, relying on pre-standard semantics for rvalue
> references, and missing out several C++11 headers.  This patch
> corrects those examples.
>
> This also tweaks some markup in the file, and adds some xml:id
> attributes to ensure stable anchors when the HTML is regenerated, so
> the link above will become
> http://gcc.gnu.org/onlinedocs/libstdc++/manual/backwards.html#backwards.third.support_cxx11
> and stay the same in future.
>
>        * doc/xml/manual/backwards_compatibility.xml: Fix autoconf tests for
>        C++11 compiler features and library headers. Add stable id
>        attributes. Use <filename> element for headers and surround in angle
>        brackets. Use <classname> for classes.
>        * doc/html/*: Regenerate.
>
> Committed to trunk.


Today I discovered that those autoconf examples written by Benjamin
are included in the autoconf archive:
http://www.gnu.org/software/autoconf-archive/ax_cxx_compile_stdcxx_0x.html

The C++11 headers one is a no-brainer, my fixes are correct and I'll
submit an update to the archive.  For the baseline language coverage
test, do we want to keep the version in the manual consistent with the
one in the archive?  Or update the archive to use the extended test I
put in the manual?

I think Alisdair Meredith has a nice little example which exercises
almost all the new language features in C++11, which would make a
great autoconf test for full language coverage (except I don't think
G++ would pass it yet, if it uses delegating constructors).