Gutenprint 5.2.5 has been released on February 11, 2010. Renaming the ebuild and the CFLAGS patch solves the problem. Reproducible: Always Steps to Reproduce:
Created attachment 220879 [details, diff] missing in $FILESDIR copy of gutenprint-5.2.3-CFLAGS.patch or, more elegant, sed s/5.2.3/5.2.5/g < gutenprint-5.2.3-CFLAGS.patch > gutenprint-5.2.5-CFLAGS.patch