Rename JCR_LIST to JCR_END in crtend.c.

This is more consistent with the names used for .ctor and .dtor
symbols and better reflects JCR_END's role.

Reviewed by: andrew
Obtained from: CheriBSD
MFC after: 2 weeks
Sponsored by: DARPA
Differential Revision: https://reviews.freebsd.org/D27125