make: empty() and friends on loop variables

[Edgar Fuß <ef%math.uni-bonn.de@localhost>]

It appears to me that empty(), defined() etc. do not work on .for loop 
variables, at least not on NetBSD 7's make and bmake-20150505.
Assigning the loop variable to anothe rintermediate var seems tu cure it.

.for i in aXa bYb
.if defined(i)
.info DEFINED
.else
.info UNDEFINED
.endif
.if empty(i:M*X*)
.info ${i}: NO
.else
.info ${i}: YES
.endif
j:= ${i}
.if empty(j:M*X*)
.info ${j}: NO
.else
.info ${j}: YES
.endif
.endfor

My guess would be that the logic that magically substitutes i with 
:U<loop value> misses the defined(i) case.