Fix a bug in sandbox timing sample collection: actually collect samples.
Implement a new '-X' argument to procstat(1), which requests eXtended timing
information on sandboxes when using '-S' and '-R'.  Min, max, mean and median
times from the current sample ring are printed for each object or method.
Rename current MIN/MAX columns to LMIN/LMAX reflecting that they are
'lifetime' rather than sample statistics, which are SMIN/SMAX/SMEAN/ SMEDIAN.
Update libc_cheri makefile for changes to libcheri.
Merge branch 'master' of https://github.com/CTSRD-CHERI/cheribsd