automake/220: if foo rules evaluating true when no else clause present

[robert dot collins at itdomain dot com dot au]

>Number:         220
>Category:       automake
>Synopsis:       if foo rules evaluating true when no else clause present
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    tromey
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Mon Aug 13 05:31:00 PDT 2001
>Closed-Date:
>Last-Modified:
>Originator:     rbtcollins@itdomain.com.au
>Release:        1.4-pl
>Organization:
>Environment:
debian-unstable
>Description:
The following rule

if USE_SNMP
SNMPSOURCE = snmp_core.c snmp_agent.c
endif

resulted in a makefile containing
SNMPSOURCE = snmp_core.c snmp_agent.c
when USE_SNMP was false.

the following rules

if USE_SNMP
SNMPSOURCE = snmp_core.c snmp_agent.c
else
SNMPSOURCE =
endif

worked correctly (only define SNMPSOURCE when USE_SNMP is true).

This used to work correctly, so I'd call it a regression. I'm mailing in
case this is by design, in which case I'll go hit up all my .am files :]
Otherwise, if it's a bug let me know and I'll generate a PR and
testcase.
>How-To-Repeat:
See description.
>Fix:

>Release-Note:
>Audit-Trail:
>Unformatted: