meson: Change default buildtype to debugoptimized

This matches the Autoconf default (-O2 + debug) better.  The previous
default setting "release" used -O3, which resulted in different
compiler warnings.  At least for now, we want to avoid such
divergence.

Discussion: https://www.postgresql.org/message-id/flat/CAFj8pRBJD_Y-XcqwXSbWS24z%2B84FFX7ajhCan9ixc_m4bD63sA%40mail.gmail.com

doc/src/sgml/installation.sgml

@@ -3001,7 +3001,7 @@ ninja install
       <listitem>
        <para>
         This option can be used to specify the buildtype to use; defaults to
-        <option>release</option>.  If you'd like finer control on the debug
+        <option>debugoptimized</option>.  If you'd like finer control on the debug
         symbols and optimization levels than what this option provides, you
         can refer to the <option>--debug</option> and
         <option>--optimization</option> flags.

meson.build

@@ -18,7 +18,7 @@ project('postgresql',
   default_options: [
     'warning_level=1', #-Wall equivalent
     'b_pch=false',
-    'buildtype=release',
+    'buildtype=debugoptimized', # -O2 + debug
     # For compatibility with the autoconf build, set a default prefix. This
     # works even on windows, where it's a drive-relative path (i.e. when on
     # d:/somepath it'll install to d:/usr/local/pgsql)