https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80782
--- Comment #12 from Iain Sandoe <iains at gcc dot gnu.org> --- AFAIK the use of the clang assembler (i.e. calling cctools as which then spawns clang -cc1as) is working on all open branches (and on the closed 6.5). please could you be more specific about exactly what's not working? - i.e if you're on an older version of the OS. - version of Xcode. Note that the default for which assembler backend is called does depend on the Xcode version.
