Re: [Ada] Reenable parallel build

[Arnaud Charlet <charlet at adacore dot com>]

> Is there any reason why parallel build is disabled in
> gcc/ada/Makefile.in? It seems to come from an old commit:

The old commit did not fully document the reasons indeed, but I did
actually recently investigate where this comment came from, and it is
actually still relevant: the gnattools target is not safe wrt parallel
builds (and there may be also an issue if gnatlib and gnattools are
run in parallel), so your patch is not OK, unfortunately.

The comment could be updated with something like:

# Tell GNU make not to run this directory in parallel when building gnattools
# or gnatlib, since not all of the required dependencies are present for
# these targets.
.NOTPARALLEL:

I have some local changes (not fully tested, and not committed anywhere)
that might slightly improve things in this area (by running a single
gnatmake command to build all gnattools to avoid having multiple gnatmake
run in parallel, generating the same objects), but still need some refinements
and testing.

Arno