CMake: clang: disable -Wmissing-braces if it is broken.
CMake: clang: disable -Wmissing-braces if it is broken.

See https://bugs.llvm.org/show_bug.cgi?id=21629
See https://reviews.llvm.org/rL314838

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