ghostscript: add dependency for pnglibconf.h
    
When using parallel make jobs, we need to be sure that
pnglibconf.h is created before we try to reference it,
so add a rule to png.mak.

Upstream-Status: Pending
    
Signed-off-by: Joe Slater <jslater@windriver.com>

--- a/base/png.mak
+++ b/base/png.mak
@@ -81,6 +81,8 @@ png.config-clean :
 $(pnglibconf_h) : $(PNGSRC)scripts$(D)pnglibconf.h.prebuilt
 	$(CP_)  $(PNGSRC)scripts$(D)pnglibconf.h.prebuilt $(pnglibconf_h)
 
+$(MAKEDIRS) : $(pnglibconf_h)
+
 PDEP=$(AK) $(pnglibconf_h) $(MAKEDIRS)
 
 png_1=$(PNGOBJ)png.$(OBJ) $(PNGOBJ)pngmem.$(OBJ) $(PNGOBJ)pngerror.$(OBJ) $(PNGOBJ)pngset.$(OBJ)