autoconf: Fix AC_STRUCT_DIRENT_D_TYPE being used before AC_PROG_CC.
autoconf: Fix AC_STRUCT_DIRENT_D_TYPE being used before AC_PROG_CC.

That was incorrect, because checking the dirent type already requires
a working compiler.

It had the effect that setting e.g. `: ${CFLAGS=""}` before `AC_PROG_CC`
as per `AC_PROG_CC`'s documentation would have no effect, because
`AC_STRUCT_DIRENT_D_TYPE` would automatically set CFLASGS.

(In a followup commit `: ${CFLAGS=""}` will be used, so it's important
to get this working first.)

ehmry/nix,dtzWill/nix,pikajude/nix,NixOS/nix,NixOS/nix,rycee/nix,NixOS/nix,ehmry/nix,ehmry/nix,dtzWill/nix,NixOS/nix,ehmry/nix,pikajude/nix,ehmry/nix,rycee/nix,dtzWill/nix,rycee/nix,dtzWill/nix,rycee/nix,NixOS/nix,pikajude/nix,rycee/nix,ehmry/nix,dtzWill/nix