building debian packages from source fails on master

[ggorman]

Following instructions to build debian packages from:
https://apt.llvm.org/building-pkgs.php

debuild -us -uc -b

fails with the error (tail only)

make[1]: Leaving directory '/home/devito/build/llvm-toolchain-snapshot-10~+20191116064212+584704c725a'
   debian/rules override_dh_install
make[1]: Entering directory '/home/devito/build/llvm-toolchain-snapshot-10~+20191116064212+584704c725a'
dh_install -p libclang-common-10-dev usr/lib/llvm-10/lib/cmake/polly/*.cmake usr/lib/llvm-10/lib/cmake/polly
rm -rf debian/tmp/usr/lib/llvm-10/lib/cmake/polly/*.cmake
dh_install --fail-missing
dh_install: Please use dh_missing --list-missing/--fail-missing instead
dh_install: This feature will be removed in compat 12.
dh_missing: usr/lib/llvm-10/lib/libomptarget-nvptx.a exists in debian/tmp but is not installed to anywhere
dh_missing: missing files, aborting
        The following debhelper tools have reported what they installed (with files per package)
         * dh_install: clang-10 (10), clang-10-doc (2), clang-10-examples (0), clang-format-10 (10), clang-tidy-10 (4), clang-tools-10 (63), clangd-10 (2), libc++-10-dev (3), libc++1-10 (2), libc++abi-10-dev (4), libc++abi1-10 (2), libclang-10-dev (74), libclang-common-10-dev (14), libclang-cpp1-10 (0), libclang-cpp10 (3), libclang1-10 (2), libfuzzer-10-dev (0), liblld-10 (10), liblld-10-dev (1), liblldb-10 (2), liblldb-10-dev (5), libllvm-10-ocaml-dev (2), libllvm10 (1), libomp-10-dev (8), libomp-10-doc (0), libomp5-10 (2), lld-10 (10), lldb-10 (10), llvm-10 (124), llvm-10-dev (199), llvm-10-doc (1), llvm-10-examples (0), llvm-10-runtime (5), llvm-10-tools (21), python-clang-10 (1), python-lldb-10 (1), python3-lldb-10 (1)
        If the missing files are installed by another tool, please file a bug against it.
        When filing the report, if the tool is not part of debhelper itself, please reference the
        "Logging helpers and dh_missing" section from the "PROGRAMMING" guide for debhelper (10.6.3+).
          (in the debhelper package: /usr/share/doc/debhelper/PROGRAMMING.gz)
        Be sure to test with dpkg-buildpackage -A/-B as the results may vary when only a subset is built
        For a short-term work-around: Add the files to debian/not-installed
dh_install: dh_missing --fail-missing returned exit code 2
debian/rules:759: recipe for target 'override_dh_install' failed
make[1]: *** [override_dh_install] Error 25
make[1]: Leaving directory '/home/devito/build/llvm-toolchain-snapshot-10~+20191116064212+584704c725a'
debian/rules:286: recipe for target 'binary' failed
make: *** [binary] Error 2
dpkg-buildpackage: error: debian/rules binary subprocess returned exit status 2
debuild: fatal error at line 1152:
dpkg-buildpackage -rfakeroot -us -uc -ui -b failed