CI: add clang scan-build job. Any issues => failed build.
CI: add clang scan-build job. Any issues => failed build.

The obvious downside is that clang-analyzer is not too great.
The obvious upside is that clang-analyzer has very high SNR.

LebedevRI/rawspeed,darktable-org/rawspeed,darktable-org/rawspeed,LebedevRI/rawspeed,darktable-org/rawspeed,darktable-org/rawspeed,darktable-org/rawspeed,LebedevRI/rawspeed,LebedevRI/rawspeed,LebedevRI/rawspeed