Which test were you running?
Do you have the tests/testrun directory? If so, preserve a tarball of that in case it's needed.
Run "threads" in dbx, and do a "where" in each thread:
Segmentation fault in noname.strlen [/usr/lib/libs.a] at 0xd0335680 ($t14) 0xd0335680 (strlen) 89030000 lbz r8,0x0(r3)
Strictly speaking, I can't rule out a bug in AIX's strlen(), but the odds that that's what you want us looking at are infinitesimally small.