Bug#962630: Acknowledgement (dovecot: FTBFS: test failures on 32-bit ARM)

Based on https://lists.debian.org/debian-glibc/2011/09/msg4.html, it appears that adding -funwind-tables to CFLAGS solves the problem on 32-bit arm systems. AFAICT, this is not documented in the gcc manual or the docs for backtrace(3). Adding -rdynamic to LDFLAGS makes the stack traces actual

Bug#962630: Acknowledgement (dovecot: FTBFS: test failures on 32-bit ARM)

Initial testing suggests that adding libunwind-dev to build-deps resolves this issue.