Bug#893023: librsl FTBFS with flex 2.6.4-6

[Ileana Dumitrescu]

librsl is only compatible with flex versions <= 2.5. I updated the packaging to change the build dependency to flex-old, which uses flex version 2.5.4a-10.1. The package now builds successfully with all architectures, including riscv. I think this bug should be closed, as the librsl upstream version 1.43 has not been updated since 2013.

Ileana Dumitrescu