Mention --without-CXX option in online help.

src/configure.in

@@ -238,7 +238,7 @@ dnl We exclude tcl support unless we override it with --with-tcl
 AC_MSG_CHECKING(setting USE_TCL)
 AC_ARG_WITH(
    tcl,
-   [  --with-tcl              use tcl ],
+   [  --with-tcl              build Tcl interfaces and pgtclsh ],
    [
 	case "$withval" in
 	y | ye | yes)		USE_TCL=true; USE_TK=true; AC_MSG_RESULT(enabled) ;;
@@ -270,7 +270,7 @@ dnl We exclude perl support unless we override it with --with-perl
 AC_MSG_CHECKING(setting USE_PERL)
 AC_ARG_WITH(
    perl,
-   [  --with-perl             use perl ],
+   [  --with-perl             build Perl interface ],
    [
 	case "$withval" in
 	y | ye | yes)	USE_PERL=true; AC_MSG_RESULT(enabled) ;;
@@ -385,7 +385,8 @@ AC_SUBST(MULTIBYTE)
 dnl Check for C++ support (allow override if needed)
 HAVECXX='HAVE_Cplusplus=true'
 AC_ARG_WITH(CXX,
-    [  --with-CXX=compiler     use specific C++ compiler],
+    [  --with-CXX=compiler     use specific C++ compiler
+  --without-CXX           prevent building C++ code ],
     [
 	case "$withval" in
 	"" | y | ye | yes)