Seems that dev-lang/spidermonkey-1.8.5's tarball was again built with old autotools: [snip] >>> Source prepared. >>> Configuring source in /home/tmp/portage/dev-lang/spidermonkey-1.8.5/work/js-1.8.5 ... * econf: updating js-1.8.5/js/src/build/autoconf/config.guess with /usr/share/gnuconfig/config.guess * econf: updating js-1.8.5/js/src/build/autoconf/config.sub with /usr/share/gnuconfig/config.sub * econf: updating js-1.8.5/js/src/ctypes/libffi/config.guess with /usr/share/gnuconfig/config.guess * econf: updating js-1.8.5/js/src/ctypes/libffi/config.sub with /usr/share/gnuconfig/config.sub ./configure --prefix=/usr --build=x86_64-pc-linux-gnu --host=x86_64-pc-linux-gnu --mandir=/usr/share/man --infodir=/usr/share/info --datadir=/usr/share --sysconfdir=/etc --localstatedir=/var/lib --libdir=/usr/lib64 --enable-jemalloc --enable-readline --enable-threadsafe --with-system-nspr --disable-static --disable-tests configure: error: threadsafe: invalid feature name [/snip]
Please add always your emerge --info and full build log as attachment
Simple fix is to just export LC_ALL="C" to ensure failure does not occur, same solution is used in all mozilla products.
usually these things are caused by doing [a-zA-Z0-9] matches instead of [[:alpha:]0-9] somewhere in the build mechanism.
Thanks for reporting, bugs have been addressed if problem persists do not hesitate to reopen.