graphics/darktable: fix broken build, data/kernels/ related
This patch is to fix this problem:
| CMake Error at data/kernels/CMakeLists.txt:34 (foreach):
| Unknown argument:
| /usr/ports/graphics/darktable/work/darktable-3.0.0/data/kernels/atrous.cl
Approved by: portmgr@ (blanket approval to fix broken builds)
Note that his revealed a Tools/scripts/mfh bug where it does not currently
check out the port directory, but only files/.
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=246336
