make rules when creating multiple files

[Thomas Klausner <wiz%NetBSD.org@localhost>]

Matthew Green provided the following analysis for PR 45126 (parallel
build breakage in Kerberos):

----- Forwarded message from matthew green <mrg%eterna.com.au@localhost> -----

i think i may have figured out the cause of this.  i noticed that
my build tree had hdb_asn1.h as a zero length file.  after a little
bit of red-herring with seeing a similar zero length file in the
src/compat build, i come across the rules in
src/crypto/external/bsd/heimdal/Makefile.rules.inc:

${ASN1_FILES.${src}} ${src:.asn1=_asn1.hx} ${src:.asn1=_asn1-priv.hx}: ${src} \
                                        ${src:.asn1=.opt} ${TOOL_ASN1_COMPILE}
        ${TOOL_ASN1_COMPILE}                    \
                ${ASN1_OPTS.${src}}             \
                --option-file=${.ALLSRC:[2]}    \
                ${.ALLSRC:[1]} ${src:.asn1=_asn1}


this rule will run the asn1_compile multiple times when it infact
only wants to be run once.  i'm not sure how this is causing zero
length files to be created but this rule is, AFAIK, broken.

i don't have a fix.


.mrg.

----- End forwarded message -----

What is the correct fix?
 Thomas