I ran the test case on an armhf machine with gdb/gdb-multiarch 7.7.1-0ubuntu5~14.04.2 from trusty-proposed, and it works well now. I also copied the binary, libraries, and core dump to an amd64 machine and ran gdb-multiarch there, with the same result. So for this purpose, the trusty-proposed binary works fine now.
I ran the test case on an armhf machine with gdb/gdb-multiarch 7.7.1-0ubuntu5~ 14.04.2 from trusty-proposed, and it works well now. I also copied the binary, libraries, and core dump to an amd64 machine and ran gdb-multiarch there, with the same result. So for this purpose, the trusty-proposed binary works fine now.