Ah, in the work directory, I also found the following... will look deeper ...
richard@devzone:/tmp/pkgsrc/print/poppler-cpp/work$ find . -name '*.h' -exec grep ICONV_CONST {} \; -print
#define ICONV_CONST const
./poppler-0.20.5/config.h
/* #undef _GLIBCXX_ICONV_CONST */
./.buildlink/gcc47/include/c++/x86_64-sun-solaris2.11/32/bits/c++config.h
/* #undef _GLIBCXX_ICONV_CONST */
./.buildlink/gcc47/include/c++/x86_64-sun-solaris2.11/bits/c++config.h
/* #undef ICONV_CONST */
./.buildlink/gcc47/lib/gcc/x86_64-sun-solaris2.11/4.7.2/plugin/include/auto-host.h