`VAR != val' in make(1) executes `val' everytime the makefile is parsed,
which a) slows down operations across the whole ports tree and b) may print
warnings from such commands.
`VAR = $$(val)', given VAR ends up in a shell command, will be run during
builds.
Switch to the latter to avoid slowdown/noise for porters, even though this
means that ports like devel/xsd now run the same pkg-config command on
every cc(1) invocation rather than just ones in the makefile.
(Most but not all ports do it this way.)
Pointed out by naddy
OK rsadowski naddy
0f7d604198