Re: [RFC] building postgres with meson - v12

Hi,

Attached is v12 of the meson patchset. Lots of improvements:

- initial set of docs for building with meson, contributed by Samay

- PGXS, .pc generation for extensions, making macos tests work when SIP is
  enabled, precompiled headers support are all now separate commits

  as suggested by Peter Eisentraut

- aix, solaris builds work now (both on gcc only)

- most of the operating system specific considerations are now collected in
  one place

  There's still the odd check around, but it's mostly for stuff where it seems
  to make sense to leave decentralized (e.g. do we need to invoke the dtrace
  binary on darwin, using wldap32 on windows, ...)

- split out the existing PG_SYSROOT selection logic from darwin's template
  into src/tools/darwin_sysroot

  Peter E. rightfully complained that the logic I had so far wasn't
  equivalent, and it's finnicky enough that it doesn't seem like a good idea
  to have two copies. Not sure about the location, perhaps it should be in
  config/ instead?

- loads of cleanups, rebasing, etc


The known things that I think need to be fixed before we could consider test
driving this on a larger scale are:

- the various global variables assembled in the toplevel meson.build need
  comments explaining them (e.g. cflags, cflags_sl, ...)

- choice of semaphore API needs to be cleaned up, that should be easy now, but
  I thought that I needed to get a new version out first

- there's a few configure tests denoted with FIXMEs, most importantly I
  haven't caught up to the PGAC_LDAP_SAFE

Greetings,

Andres Freund