diagnostics: get_option_html_page fixes

While testing the --with-documentation-root-url= changes, I run into
[Wreturn-type] URL pointing to gfortran documentation where it obviously
isn't documented.  The following patch updates the list of options to match
reality (on the other side -Wconversion-extra is gfortran only option
documented in gfortran.texi).

Or, perhaps better use the attached patch instead, which doesn't have a
hardcoded list and instead uses the flags?  I went through options.c
and the updated list of options matches exactly the cases where CL_Fortran
is set for "-W*" options together with CL_C and/or CL_CXX (ok, there is also
-Wall and -Wextra, but hopefully we don't emit [Wall] or [Wextra] for
anything).

2020-05-04  Jakub Jelinek  <jakub@redhat.com>

	* opts.c (get_option_html_page): Instead of hardcoding a list of
	options common between C/C++ and Fortran only use gfortran/
	documentation for warnings that have CL_Fortran set but not
	CL_C or CL_CXX.

gcc/ChangeLog

+2020-05-04  Jakub Jelinek  <jakub@redhat.com>
+
+	* opts.c (get_option_html_page): Instead of hardcoding a list of
+	options common between C/C++ and Fortran only use gfortran/
+	documentation for warnings that have CL_Fortran set but not
+	CL_C or CL_CXX.
+
 2020-05-07  Jakub Jelinek  <jakub@redhat.com>
 
 	* BASE-VER: Set to 10.1.1.

gcc/opts.c

@@ -3141,25 +3141,15 @@ get_option_html_page (int option_index)
     return "gcc/Static-Analyzer-Options.html";
 
 #ifdef CL_Fortran
-  if (cl_opt->flags & CL_Fortran)
-    {
-      switch (option_index)
-	{
-	default:
-	  /* Most Fortran warnings are documented on this page.  */
+  if ((cl_opt->flags & CL_Fortran) != 0
+      /* If it is option common to both C/C++ and Fortran, it is documented
+	 in gcc/ rather than gfortran/ docs.  */
+      && (cl_opt->flags & CL_C) == 0
+#ifdef CL_CXX
+      && (cl_opt->flags & CL_CXX) == 0
+#endif
+     )
     return "gfortran/Error-and-Warning-Options.html";
-
-	case OPT_Wdate_time:
-	case OPT_Wconversion:
-	case OPT_Wconversion_extra:
-	case OPT_Wmissing_include_dirs:
-	case OPT_Wopenmp_simd:
-	  /* These warnings are marked in fortran/lang.opt as
-	     "Documented in C" and thus use the common
-	     Warning-Options page below.  */
-	  break;
-	}
-    }
 #endif
 
   return "gcc/Warning-Options.html";