bug#64937: boot time on Linux

[Bruno Haible]

Paul Eggert wrote:
> This patch does not address the problem for Alpine, nor I suspect for 
> Android. I suppose Alpine could use the timestamp of /var/run/utmp (or 
> is that /run/utmp?) but I don't know how 'configure' would reliably 
> detect it's being built or cross-built for Alpine. I'll cc this to 
> Natanael Copa, who does the Alpine ports for Emacs, to see whether he 
> can give advice.

For Alpine Linux, in Gnulib, I've used the following approach:
Read the entire contents of /var/run/utmp, and if it contains no entry
with ut_type == BOOT_TIME, look at the time stamp of some files,
in particular /var/run/utmp. It doesn't require a configure test.

Bruno