make: Entering directory `/tmp/djerome-ttylinux-9db9595/ttylinux-build/build/packages/gmp-4.3.2'
./gen-psqr 64 0 >mpn/perfsqr.h || (rm -f mpn/perfsqr.h; exit 1)
./gen-psqr: /lib/libc.so.6: version `GLIBC_2.14' not found (required by ./gen-psqr)
Sure enough, the Debian 5.0.7 system in question has glibc 2.7 in /lib. But I don't think that's where it should be looking.
I've successfully gotten around this issue by compiling glibc 2.14 from source and replacing the stock 2.7 that ships with Debian 5.0.7 amd64, but this seems incredibly hacky as the cross-tool chain should have these libraries available (looking closely, they're there, but the path doesn't seem to be passed correctly into the build for gmp).