because stdio.h isn't included, it thinks that fprintf is an extern.

pdf2png.c: In function `main':
pdf2png.c:47: warning: implicit declaration of function `fprintf'
pdf2png.c:47: warning: nested extern declaration of `fprintf'
pdf2png.c:47: error: `stderr' undeclared (first use in this function)
pdf2png.c:47: error: (Each undeclared identifier is reported only once
pdf2png.c:47: error: for each function it appears in.)
pdf2png.c:64: warning: nested extern declaration of `fprintf'
pdf2png.c:68: warning: nested extern declaration of `fprintf'
pdf2png.c:72: warning: nested extern declaration of `fprintf'
pdf2png.c:85: warning: nested extern declaration of `fprintf'

Index: test/pdf2png.c
===================================================================
RCS file: /cvs/cairo/cairo/test/pdf2png.c,v
retrieving revision 1.1
diff -u -p -u -r1.1 pdf2png.c
--- test/pdf2png.c      8 Dec 2005 00:06:12 -0000       1.1
+++ test/pdf2png.c      9 Dec 2005 18:22:37 -0000
@@ -24,6 +24,7 @@
  */

 #include <stdlib.h>
+#include <stdio.h>
 #include <poppler.h>

 #define FAIL(msg)                                                      \