A small note on the portability of cmake

I tried to build cmake on OpenBSD running on my old HPPA hardware,
not because I cared about cmake per se but because it's a dependency
of something I did care about.  Failed miserably.  It turns out cmake has
a hard dependency on libuv which (a) has a hard dependency on atomic ops
and (b) according to its own docs, doesn't really care about any
platforms other than Linux/macOS/Windows and maybe FreeBSD.  It looks
to me like switching to that toolchain would greatly constrict our
ability to build on non-mainstream platforms, simply because the tools
themselves fail to build.

Just sayin' ...

			regards, tom lane