Fix builds of PDFio under libcups directory.

Makefile

@@ -1,7 +1,7 @@
 #
 # Top-level Makefile for IPP sample implementations.
 #
-# Copyright © 2014-2023 by the Printer Working Group.
+# Copyright © 2014-2024 by the Printer Working Group.
 #
 # Licensed under Apache License v2.0.  See the file "LICENSE" for more
 # information.
@@ -13,6 +13,7 @@ include Makedefs
 # Source directories...
 DIRS	=	\
 		libcups/cups \
+		libcups/pdfio \
 		libcups/tools \
 		server \
 		tools
@@ -24,8 +25,10 @@ DIRS	=	\
 
 all:
 	for dir in $(DIRS); do \
-		echo "======== all in $$dir ========"; \
-		(cd $$dir; $(MAKE) $(MFLAGS) CFLAGS="$(CFLAGS)" COMMONFLAGS="$(OPTIM)" all) || exit 1; \
+		if test -f $$dir/Makefile; then \
+			echo "======== all in $$dir ========"; \
+			(cd $$dir; $(MAKE) $(MFLAGS) all) || exit 1; \
+		fi; \
 	done
 
 
@@ -35,8 +38,10 @@ all:
 
 clean:
 	for dir in $(DIRS); do \
-		echo "======== clean in $$dir ========"; \
-		(cd $$dir; $(MAKE) $(MFLAGS) clean) || exit 1; \
+		if test -f $$dir/Makefile; then \
+			echo "======== clean in $$dir ========"; \
+			(cd $$dir; $(MAKE) $(MFLAGS) clean) || exit 1; \
+		fi; \
 	done
 
 
@@ -67,8 +72,10 @@ depend:
 
 install:
 	for dir in $(DIRS) examples man; do \
-		echo "======== install in $$dir ========"; \
-		(cd $$dir; $(MAKE) $(MFLAGS) prefix=$(prefix) install) || exit 1; \
+		if test -f $$dir/Makefile; then \
+			echo "======== install in $$dir ========"; \
+			(cd $$dir; $(MAKE) $(MFLAGS) prefix=$(prefix) install) || exit 1; \
+		fi; \
 	done
 
 
@@ -80,8 +87,10 @@ install:
 
 test:
 	for dir in $(DIRS); do \
-		echo "======== test in $$dir ========"; \
-		(cd $$dir; $(MAKE) $(MFLAGS) CFLAGS="$(CFLAGS)" COMMONFLAGS="$(OPTIM)" test) || exit 1; \
+		if test -f $$dir/Makefile; then \
+			echo "======== test in $$dir ========"; \
+			(cd $$dir; $(MAKE) $(MFLAGS) CFLAGS="$(CFLAGS)" COMMONFLAGS="$(OPTIM)" test) || exit 1; \
+		fi; \
 	done
 	echo "Running integration tests..."
 	test/run-tests.sh