GCC-4.6 rebuild tests

[Matthias Klose]

[ Note that GCC-4.6 will not be used for natty / 11.04, but
   we consider using this version for the O-series / 11.10 ]

A test rebuild of natty/main using the current GCC version from the trunk was 
finished last week.  While only one internal compiler error was found, some more 
build failures were seen due to new warnings and more strict frontends. A list 
of build failure can be seen at

http://people.ubuntuwire.org/~wgrant/rebuild-ftbfs-test/test-rebuild-20110111-gcc-natty.html

If a package appears in the `superseded' section, it doesn't mean that the build 
failure with GCC-4.6 is fixed.

Some comments and hints for fixes can be found at

   https://wiki.ubuntu.com/GCC4.6

Please extend the wiki page if appropriate.

To work on the build failures, please use either the gcc-snapshot package from 
natty or the gcc-4.6 package from the ubuntu-toolchain-r/test PPA.

A large number of build failures is seen for packages building with -Werror. The 
compiler packages above were changed to add a -Wno-error=unused-but-set-variable 
when -Werror is found. Despite this local change the these packages need to 
build without this local change.

   Matthias

PS: Fixing build failures with GCC-4.5 in natty should still have priority ;)