Just had this happen on a 64 bit box after seeing it on a 32 bit virtual machine:

conftest[6750]: segfault at 1 ip 00007f1978ec2739 sp 00007fff4de65190 error 4 in libc-client.so.1.0.0[7f1978e84000+fb000]
conftest[18209]: segfault at 1 ip 00007f034a1de739 sp 00007fff522332a0 error 4 in libc-client.so.1.0.0[7f034a1a0000+fb000]
conftest[30093]: segfault at 1 ip 00007f6f163ea739 sp 00007fff6cd3a0c0 error 4 in libc-client.so.1.0.0[7f6f163ac000+fb000]
conftest[9687]: segfault at 1 ip 00007f9392238739 sp 00007fff4cc9a600 error 4 in libc-client.so.1.0.0[7f93921fa000+fb000]

Seems to occur when emerging PHP 5.3.15 at ./configure though I have seen no problems with the php binary itself.