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I'm not sure is there any package on extras-devel using gcc-4.6 or g++4.6.

But here comes instructions how to use g++-4.6 with autobuilder.
1) debian/control
-Architecture: any
+Architecture: armel
(because compiler on builder is only arm-to-arm)

2) debian/control
+Build-Depends: g++-4.6, binutils2.22
(because g-4.6 needs binutils2.22)

3) debian/control
+Depends: libstdc++6 (>4.6.1)
(I hope this will not break existing applications. I have tested only with one device and didn't seen any failures)

4) Makefile (or configure, configure.ac ...)
-CXX = g++
+CXX = g++-4.6
+LDFLAGS += -B /usr/binutils2.22/bin
(This works better than tuning PATH during debian/rules with PATH=/usr/binutils2.22/bin:$PATH)

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And I'm slipping topic again, but seems same approach could work even builder has gcc-4.7 (maybe even +thumb).