bug#68808: subsecond mtime discovery code insufficient

[Erik A Johnson]

I found the problem!  The default GNU make on macOS (even Sonoma) is 3.81 from 
2006!  The configure script for GNU make versions <4.0 did not have the right 
test for subsecond resolution in the macOS stat() function, so 3.81 was built 
with resolution only to the second, not subsecond, thus needing at least one 
second sleep.  (Why, then, does Apple continue to include 3.81 in the software 
18 years later? Beyond me.)

Installing the most recent release of GNU make (4.4.1) fixes the problem.  
Tests all run successfully.

Erik


----------------------------------------

Details ... With make 3.81, if I create a simple Makefile with

        foo: bar
                touch foo

then

        touch foo
        touch bar
        make

should make (touch) foo because bar is newer.  However, if these are done 
immediately after each other

        touch foo; touch bar; make

then, most of the time, make just responds with "make: `foo' is up to date."  
The following

        n=0; while make | grep -q 'up to date'; do touch foo; touch bar; printf 
.; n=$(($n+1)); done; echo $n

varies from a handful of trials to several thousand trials before foo's mtime's 
integer is one less than bar's mtime's integer.