buildroot 2009.08-rc3 ./toolchain/external-toolchain/ext-tool.mk checks if 'lib/ld-linux.so.*' is present in the toolchain's sysroot. This is fine for x86 system, but this check fails for x86_64 systems and crosstool-ng toolchains. Here you have 'lib/ld-linux-x86-64.so.2 -> ld-2.9.so'. The check could/should be modified to 'lib/ld-linux*.so.*'
Ok, I confirm the issue and agrees with your proposal. I've written a patch implementing this, but unfortunately, the build still doesn't work for me due to mix between the host x86-64 C library and the target x86-64 C library. I'll try to work these out.
Fixed by http://git.buildroot.net/buildroot/commit/?id=914f19ca1ea648d451bfa2ab232dbf1cc1fed351.