The ./configure script seems to be badly implemented regarding detection of spidermonkey -- the only libs it searches for at the moment is libjs (current stable provides libmozjs, and testing provides libmozjs185); and the vast majority of searches seem to relate to an embedded copy instead of a system copy (this is from reading through the ./configure script directly). Furthermore, the tarball does not contain the extra .m4 files used to build configure (aclocal.m4 lists them for inclusion but I could not find spidermonkey.m4 anywhere).
That's correct, upstream doesn't feel like distributing their .m4 macros with tarball, instead they provide generated blob.. (btw, macros are here http://hg.sim.no/simacros/default/file/c9c336b0ae4f) Please provide usual info (emerge --info, build log)
Well i found this out by reading the configure script and aclocal.m4 directly... ill do a test emerge and attach my --info and config.log tomorrow.
UNreproducable. Please provide info and reopen.