mtime of installed files

[Ludovic Courtès]

Hello,

Background: Guile 1.9/2.0 has an auto-compilation feature whereby if a
source file has no corresponding object file in the search path, or if
the object file is older than the source file, then the source file is
automatically recompiled and stored in ~/.cache/guile/ccache.

Packages that use Guile can also choose to pre-compile all their source
files and install both the source and object files.  This saves the need
for users to auto-compile the source.  (This is what Guile does with its
own source files.)

For this to work, we need “make install” to guarantee the relation
mtime(installed-object) >= mtime(installed-source), assuming we have
mtime(builddir-object) >= mtime(srcdir-source), which will always be the
case unless the computer’s clock is skewed.

Do Automake-generated makefiles provide such a guarantee?  Regardless of
the ‘make’ implementation, OS, etc.?

Thanks,
Ludo’.