uClibc:
 * consider FREETZ_TARGET_UCLIBC_SUPPORTS_libubacktrace-option while building uClibc
 * refs r10542
 * fixes #2322

Note: users experiencing problems like that reported in #2322 should either
 * rebuild the target toolchain, or
 * (workaround) execute the following command {{{rm toolchain/target/include/execinfo.h toolchain/target/libubacktrace*}}}
In both cases the affected package (=samba) should be rebuilt afterwards.


git-svn-id: file:///var/svn/freetz/trunk@11521 149334a1-2f27-0410-a3b9-fc62619ac1e6