FreeSWITCH-codec2

FS-7088 #resolve Set flag to enable core dump from non-root users.

When FreeSWITCH is running as a non-privileged user, we need to enable
PR_SET_DUMPABLE for it to be able to generate core dumps.

Instead of a generic __linux__ check, there's a new configure.ac flag
to check directly for prctl.h, which could also be used in other
places in the code.