[bug #49093] ifdef checks for non-empty value, not definition

[Paul D. Smith]

Update of bug #49093 (project make):

              Item Group:                     Bug => Documentation          
           Triage Status:                    None => Small Effort           

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Follow-up Comment #1:

What the doc is trying to say is that:


FOO =
ifdef FOO
$(info true)
endif


will not print true because FOO has no value.

However, this:


FOO =
BAR = $(FOO)
ifdef BAR
$(info true)
endif


_will_ print true.  Even though if you expanded $(BAR) you'd get the empty
string, the variable BAR is not empty (it's set to $(FOO)) and so ifdef calls
it defined.  Probably an example like this would help make the doc more
clear.

Yes, it's true that ifdef is badly named.  It should be something like "ifset"
or whatever instead.  However, it works as intended and so does the origin
function value "undefined"; they have had these inconsistent meanings for 20+
years now; they're not going to change.

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