x11/cde: Fix build under 14-CURRENT

Under 14-CURRENT MALLOC_PRODUCTION is not set which puts malloc() into
debug mode. In debug mode malloc() enables opt.junk to write junk to
newly malloc()ed heap in order to help developers discover memory
allocation bugs. Unfortunately CDE's dtinfogen assumes newly malloc()ed
memory is zero filled (i.e. not filled with junk), resulting in
"flex scanner jammed". This likely causes parsing of the junk past the
end of any legitimate statements. This affects stock 14-CURRENT without
MALLOC_PRODUCTION enabled. This is accomplished by setting the
make environment variable MALLOC_CONF=junk:false. See malloc(3) for
a complete description of MALLOC_CONF=junk:false.

MFH: 2022Q1