Both nspr-4.9.2 and nspr-4.9.4 fail to build on arm (probably on x86 as well, but I haven't tested that). The problem is that nspr needs an autoconf 2.1, which is obsolete though still in the tree, and that version of autoconf is not an explicit dependency in the ebuild. Once autoconf-2.13 has been emerged the packages build correctly.
Created attachment 352584 [details] autoconf error message
Both left the tree on June 19. Could you try again with 4.9.5 or better? Also, if that still fails in the same way, then please: 1) attach the entire build log to this bug report. 2) post your `emerge --info' output in a comment. 3) again, attach the autoconf.log to this bug report.