Portability report: ninja

Meson depends on ninja, so it behooves us to look into portability
of ninja if we're considering migrating to meson as the build system.
I tried it out quickly on some ancient platforms, and here's what
I found.

1. The documentation is kinda sucky, eg it fails to explain how
to run ninja's own regression tests. I ended up with this
reverse-engineered recipe:

git clone git://github.com/ninja-build/ninja.git
cd ninja
git checkout release
./configure.py --bootstrap
./ninja ninja_test
./ninja_test
sudo cp ninja /usr/local/bin # or location of choice

We'll probably have to include that in our own documentation.

2. You need Python to build it this way. There is also a process
for bootstrapping using cmake, but that doesn't seem like a more
attractive dependency for old platforms. Fortunately for my
purposes here, it seems to work with fairly old Python --- I built
successfully with python 2.6.2, though not with 2.4.1.

3. You also need a C++ compiler, but really old ones will work.
I did not see any problems with g++ as old as 4.0.1, other than
some compiler warnings about non-virtual destructors.

4. It built and passed self-test on macOS Leopard (10.5.8), which is
pretty old ... but not old enough for prairiedog, which is stuck on
10.4.x. There, the build fails miserably for lack of <spawn.h>.
It looks like that was added to POSIX in 2001, so one could have
wished for it in a 2005-vintage OS; but nope, Apple took another
couple of years to get around to that. I'm not even going to bother
trying on gaur's pre-turn-of-the-century OS.

5. It built and passed self-test on Solaris 11, but failed self-test
on Solaris 10.

6. While configure.py thinks it knows what to do on AIX, it fails
on AIX 7.1 and 7.2:

Traceback (most recent call last):
File "./configure.py", line 544, in <module>
if platform.is_aix() and not platform.is_os400_pase():
File "./configure.py", line 103, in is_os400_pase
return self._platform == 'os400' or os.uname().sysname.startswith('OS400')
AttributeError: 'tuple' object has no attribute 'sysname'

Possibly the ninja guys would take a patch for that (or maybe
this is a you-need-python-3 case?). I do see /usr/include/spawn.h
on that platform, so there's room to hope it'd work.

So it's pretty clear that if we go this way, it'll be the end of
the line for support for some very old OS versions. I can't,
however, argue with the idea that it's reasonable to require
POSIX 2001 support now. Based on these results, I doubt that
ninja will give us trouble on any platform that isn't old
enough to get its drivers license.

regards, tom lane