Comment 1 for bug 218409

Gentoo devs offer a patch for this problem.

--- libpng/pngconf.h
+++ libpng/pngconf.h
@@ -323,8 +323,8 @@
      /* If you encounter a compiler error here, see the explanation
       * near the end of INSTALL.
       */
- __pngconf.h__ already includes setjmp.h;
- __dont__ include it again.;
+#warning __pngconf.h__ already includes setjmp.h;
+#warning __dont__ include it again.;
 # endif
 # endif /* __linux__ */

Patch taken from:
http://mirrors.usc.edu/pub/linux/distributions/gentoo/media-libs/libpng/files/libpng-1.2.24-pngconf-setjmp.patch