Problem with boot-time on Cygwin

[Ken Brown]

An Emacs bug report 
(https://debbugs.gnu.org/cgi/bugreport.cgi?bug=70415) has led me to look 
at gnulib's boot-time, and I discovered a problem.  I haven't studied 
the code in detail, but I looked at get_windows_boot_time in 
boot-time-aux.h and found two mistakes.  First, there is a comment 
saying that /var/run/utmp is empty on Cygwin.  This is not true, at 
least on my system.  I'm running Cygwin 3.5.3, the latest stable 
release.  I don't know if this matters, i.e., if the knowledge that 
/var/run/utmp is not empty would change anything elsewhere in the code.

Second, and more serious, is the use of /cygdrive/c to refer to the C: 
drive.  In fact, users can set the "cygdrive prefix" to anything they 
want in /etc/fstab.  For example, I use /mnt as the cygdrive prefix, so 
I would use /mnt/c for the C: drive.  The correct way to use the 
cygdrive prefix is to use /proc/cygdrive.  For example, /proc/cygdrive 
is a symlink to /mnt/ on my system.

Ken