Change mulle-sde C project to use mulle-clang compiler

You'd still need to add the runtime dependencies, this is just to get the compiler going (with .m files):

 1mulle-sde tool add mulle-clang
 2mulle-sde dep add github:mulle-objc/mulle-objc-cc
 3mulle-sde dep mark mulle-objc-cc no-link
 4mulle-sde dep mark mulle-objc-cc no-header
 5# get .m files working
 6mulle-sde env set PROJECT_DIALECT objc
 7mulle-sde env set --append PROJECT_EXTENSIONS m
 8mulle-sde env set --append MULLE_MATCH_FILENAMES '*.m'
 9mulle-sde patternfile edit 95-source--sources
10# add *.m