Change cpp usage in the Makefile to make error handling more reliable

Call cpp directly on our input task file instead of using it in a
pipeline. Not clear why this was ever done, and it obscures errors
like ENOENT (if the specified task file is missing).

Makefile

@@ -376,11 +376,10 @@ $(BDIR)/rawlist:
 		ARCHDEFS="$$ARCHDEFS -DARCH_i386_EXCLUDE_586_KERNEL"; \
 	fi; \
 	if [ "$(SOURCEONLY)"x != "yes"x ] ; then \
-		cat $(TASKDIR)/$(TASK) | \
 		cpp -nostdinc -P -undef $$ARCHDEFS $$VARIANTDEFS\
 	   		$$ARCHUNDEFS -U i386 -U linux -U unix \
 		    -DFORCENONUSONCD1=0 \
-		    -I $(TASKDIR) - - >> $(BDIR)/rawlist; \
+		    -I $(TASKDIR) $(TASKDIR)/$(TASK) >> $(BDIR)/rawlist; \
 	fi
 
     # If we're *only* doing source, then we need to build a list of all the

debian/changelog

@@ -7,6 +7,7 @@ debian-cd (3.1.18) UNRELEASED; urgency=medium
   * Add YA syslinux package to Recommends.
   * Fix handlinkg of LOGOPNG when we've got "doppelganer" initramfs files
   * Add support for debian-edu builds
+  * Change cpp usage in the Makefile to make error handling more reliable
 
   [ Didier Raboud ]
   * For stretch, swap amd64 and i386 to let the first be the norm, and the