Add support for basic NUMA awareness

Add basic NUMA awareness routines, using a minimal src/port/pg_numa.c
portability wrapper and an optional build dependency, enabled by
--with-libnuma configure option. For now this is Linux-only, other
platforms may be supported later.

A built-in SQL function pg_numa_available() allows checking NUMA
support, i.e. that the server was built/linked with the NUMA library.

The main function introduced is pg_numa_query_pages(), which allows
determining the NUMA node for individual memory pages. Internally the
function uses move_pages(2) syscall, as it allows batching, and is more
efficient than get_mempolicy(2).

Author: Jakub Wartak <jakub.wartak@enterprisedb.com>
Co-authored-by: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Reviewed-by: Andres Freund <andres@anarazel.de>
Reviewed-by: Álvaro Herrera <alvherre@alvh.no-ip.org>
Reviewed-by: Tomas Vondra <tomas@vondra.me>
Discussion: https://postgr.es/m/CAKZiRmxh6KWo0aqRqvmcoaX2jUxZYb4kGp3N%3Dq1w%2BDiH-696Xw%40mail.gmail.com

meson.build

@@ -943,6 +943,27 @@ else
 endif
 
 
+###############################################################
+# Library: libnuma
+###############################################################
+
+libnumaopt = get_option('libnuma')
+if not libnumaopt.disabled()
+  # via pkg-config
+  libnuma = dependency('numa', required: false)
+  if not libnuma.found()
+    libnuma = cc.find_library('numa', required: libnumaopt)
+  endif
+  if not cc.has_header('numa.h', dependencies: libnuma, required: libnumaopt)
+    libnuma = not_found_dep
+  endif
+  if libnuma.found()
+    cdata.set('USE_LIBNUMA', 1)
+  endif
+else
+  libnuma = not_found_dep
+endif
+
 
 ###############################################################
 # Library: liburing
@@ -3279,6 +3300,7 @@ backend_both_deps += [
   icu_i18n,
   ldap,
   libintl,
+  libnuma,
   liburing,
   libxml,
   lz4,
@@ -3935,6 +3957,7 @@ if meson.version().version_compare('>=0.57')
       'icu': icu,
       'ldap': ldap,
       'libcurl': libcurl,
+      'libnuma': libnuma,
       'liburing': liburing,
       'libxml': libxml,
       'libxslt': libxslt,