threadsnoop: look for pthread_create in libc too
threadsnoop: look for pthread_create in libc too

Since glibc 2.34, pthread features are integrated in libc directly.
Look for pthread_create there too when it is not found in libpthread.

Fixes #3623

iovisor/bcc,brendangregg/bcc,brendangregg/bcc,brendangregg/bcc,iovisor/bcc,brendangregg/bcc,iovisor/bcc,iovisor/bcc,iovisor/bcc,brendangregg/bcc