* Restore setting unroll-threshold on LLVM 9 to avoid kernel/test_rotate
hanging on avx512 capable cpus. (Closes: #980626)
* Kill hanging tests after 30 minutes.
* Let dh_shlibdeps find libpocl-devices-basic.so.
* Do not use the embedded copy of the OpenCL headers.
* Build with -fvisibility-inlines-hidden.
* Drop hidden symbols.
* Bump Standards-Version to 4.5.1, no changes needed.