Strip -Wformat-overflow=2 -Wformat-truncation=2 in debian/rules

These flags conflict with the build of libunwind leading to a build failure: CMake Error at /usr/src/packages/BUILD/libunwind/src/CMakeLists.txt:109 Compiler doesn't support generation of unwind tables if exception support is disabled. Building libunwind DSO with runtime dependency on C++ ABI library is not supported.

Signed-off-by: Dylan Aïssi dylan.aissi@collabora.com