Comment # 3 on bug 1022404 from Michal Suchanek

yes, regarding the avr-libc missing from factory that can be fixed trivially by
importing it from other project.

However, gcc refuses to build a libgcc because there is no way to specify where
the target headers and libraries should be built.

avr-libc moved from /usr/avr to /opt/cross/avr due to FHS. The exact directory
is irrelevant. Wherever it is it has libraries in ${target_prefix}/lib and
includes in ${target_prefix}/include. There is an --with-sysroot configure
option that tells gcc to look (and build) target headers and libraries in a
prefix but it insists on using {sysroot}/usr/lib and ${sysroot}/usr/include.
There is option --with-native-headers-prefix or somesuch which can change that
for headers but none for libraries.