bug#68545: warnings from GNU Make 3.81

[Eli Zaretskii]

> Cc: Po Lu <luangruo@yahoo.com>
> From: Mattias Engdegård <mattias.engdegard@gmail.com>
> Date: Wed, 17 Jan 2024 19:50:13 +0100
> 
> Building with GNU Make 3.81, which seems to be supported, gives the warnings
> 
> /Applications/Xcode.app/Contents/Developer/usr/bin/make -C java 
> bootstrap-clean
> Makefile:157: warning: overriding commands for target `&'
> Makefile:151: warning: ignoring old commands for target `&'
> Makefile:168: warning: overriding commands for target `&'
> Makefile:157: warning: ignoring old commands for target `&'
> Makefile:296: warning: overriding commands for target `&'
> Makefile:168: warning: ignoring old commands for target `&'
> 
> That version probably doesn't like '&'. Given that I'm not building anything 
> in the java/ directory anyway, perhaps  that sub-make can be avoided 
> altogether for platforms other than Android?

The &: feature was introduced in GNU Make 4.3, and we don't want to
force people to use such new versions.  So please find a different
solution for what you need to do there, one that doesn't require Make
newer than 3.81.