config.mk: use PKG_CONFIG in commented OpenBSD section

config.mk

@@ -28,8 +28,8 @@ STLDFLAGS = $(LIBS) $(LDFLAGS)
 # OpenBSD:
 #CPPFLAGS = -DVERSION=\"$(VERSION)\" -D_XOPEN_SOURCE=600 -D_BSD_SOURCE
 #LIBS = -L$(X11LIB) -lm -lX11 -lutil -lXft \
-#       `pkg-config --libs fontconfig` \
-#       `pkg-config --libs freetype2`
+#       `$(PKG_CONFIG) --libs fontconfig` \
+#       `$(PKG_CONFIG) --libs freetype2`
 
 # compiler and linker
 # CC = c99