Change ald to assemble successfully and include it in build.

While the scan of src/cmd/als.s clearly refers to ferror,
that routine is entirely missing from the scans of ald.

There are two identical ferror routines in src/cmd/adm.s and
src/cmd/apr.s printing the file name of a file that cannot be
openend.

ald calls ferror when unable to create a file. For ald to have
a similar ferror routine when creation fails appears sensible.

Therefore a similar routine is added to src/cmd/ald.s with
modifications to the variable containing the file name and
the label ferror jumps back to once done.

build/proto

@@ -23,6 +23,7 @@ dd           drwr- -1 4
         pptout   irwr- -1 13
         password frw-- -1 fs/password
         adm      frwr- -1 bin/adm
+        ald      frwr- -1 bin/ald
         apr      frwr- -1 bin/apr
         as       frwr- -1 bin/as
         b        frwr- -1 bin/b