Update man/scons.xml CheckFunc documentation for optional header and funcargs usage. [ci skip]

Author: jcbrill

CHANGES.txt

@@ -8,14 +8,15 @@ NOTE: The 4.0.0 Release of SCons dropped Python 2.7 Support
 NOTE: 4.3.0 now requires Python 3.6.0 and above. Python 3.5.x is no longer supported
 
 RELEASE  VERSION/DATE TO BE FILLED IN LATER
+
   From Ataf Fazledin Ahamed:
     - Use of NotImplemented instead of NotImplementedError for special methods
       of _ListVariable class
-  
+
   From Joseph Brill:
-    - Add an optional argument list string to configure's CheckFunc method so
-      that the generated function argument list matches the function's
-      prototype when including a header file. Fixes GH Issue #4320
+    - Fix issue #4320: add an optional argument list string to configure's CheckFunc
+      method so that the generated function argument list matches the function's
+      prototype when including a header file.
 
   From Michał Górny:
     - Remove unecessary dependencies on pypi packages from setup.cfg
@@ -25,7 +26,6 @@ RELEASE  VERSION/DATE TO BE FILLED IN LATER
       statement with stop flag enabled
 
 
-
 RELEASE 4.6.0 -  Sun, 19 Nov 2023 17:22:20 -0700
 
   From Max Bachmann:

doc/man/scons.xml

@@ -3982,15 +3982,14 @@ char function_name(void);
 </programlisting>
 
 <para>
-      The optional <parameter>funcargs</parameter> can be defined to specify an argument list for the generated
-      function invocation.
-</para>
-
-<para>
-Note: if <parameter>header</parameter> is supplied,
-  and the function_name being called takes any parameters, appropriate values for those
-  function arguments should be supplied
-  by using the <parameter>funcargs</parameter>.
+If <parameter>header</parameter> is supplied, it should <emphasis>not</emphasis> include
+the standard header file that declares <parameter>function_name</parameter> and it
+<emphasis>should</emphasis> include a dummy prototype similar to the default case.  If
+this is not possible, the optional <parameter>funcargs</parameter> argument can be used
+to specify a string containing an argument list with the same number and type of
+arguments as the prototype.  The arguments can simply be constant values of the correct
+type.  Modern C/C++ compilers reject implicit function declarations and may also reject
+function calls whose arguments are not type compatible with the prototype.
 </para>
 
 <para>