doc: Fix some gaps with the documentation related to LZ4

The upstream project is officially named "LZ4", and the documentation
was confused with the option value that can be used with DDLs supporting
this option, and the project name.

Documentation related to the configure option --with-lz4 was missing, so
add something for that.

Author: Dilip Kumar, Michael Paquier
Reviewed-by: Justin Pryzby
Discussion: https://postgr.es/m/YJaOZQDXBVySq+Cc@paquier.xyz

doc/src/sgml/catalogs.sgml

@@ -1363,7 +1363,7 @@
        The current compression method of the column.  If it is an invalid
        compression method (<literal>'\0'</literal>) then column data will not
        be compressed.  Otherwise, <literal>'p'</literal> = pglz compression or
-       <literal>'l'</literal> = lz4 compression.
+       <literal>'l'</literal> = <productname>LZ4</productname> compression.
       </para></entry>
      </row>
 

doc/src/sgml/config.sgml

@@ -8321,9 +8321,9 @@ COPY postgres_log FROM '/full/path/to/logfile.csv' WITH csv;
         <command>CREATE TABLE</command> statement can override this default
         by specifying the <literal>COMPRESSION</literal> column option.
 
-        The supported compression methods are <literal>pglz</literal> and
+        The supported compression methods are <literal>pglz</literal> and,
-        (if configured at the time <productname>PostgreSQL</productname> was
+        if <productname>PostgreSQL</productname> was compiled with
-        built) <literal>lz4</literal>.
+        <literal>--with-lz4</literal>, <literal>lz4</literal>.
         The default is <literal>pglz</literal>.
        </para>
       </listitem>

doc/src/sgml/installation.sgml

@@ -266,6 +266,14 @@ su - postgres
      </para>
     </listitem>
 
+    <listitem>
+     <para>
+      You need <productname>LZ4</productname>, if you want to support
+      compression of data with this method; see
+      <xref linkend="guc-default-toast-compression"/>.
+     </para>
+    </listitem>
+
     <listitem>
      <para>
       To build the <productname>PostgreSQL</productname> documentation,
@@ -966,6 +974,17 @@ build-postgresql:
        </listitem>
       </varlistentry>
 
+      <varlistentry>
+       <term><option>--with-lz4</option></term>
+       <listitem>
+        <para>
+         Build with <productname>LZ4</productname> compression support.
+         This allows the use of <productname>LZ4</productname> for
+         compression of table data.
+        </para>
+       </listitem>
+      </varlistentry>
+
       <varlistentry>
        <term><option>--with-ssl=<replaceable>LIBRARY</replaceable></option>
        <indexterm>