adding inherit libtool and uclibctoolize solves the problem Reproducible: Always Steps to Reproduce: 1. 2. 3.
Sorry for the delay. I added 'inherit libtool' and 'uclibctoolize' to rxvt-2.7.10-r2.ebuild, so please test and see if it compiles correctly with uclibc/hardned. Thanks for the bug report.
I have tested it before I have submitted the bug, if you added it to all versions it is ok (stable, ~arch, -* if any), you can close it