build: extend SMB_LIBRARY() to optionally take default value.

The default value defaults to "yes".
If no is specified, an optional third argument contains the
reason why building of the shared library is turned off by default.

Michael
(This used to be commit af971f79c7)

source3/m4/aclocal.m4

@@ -54,7 +54,7 @@ AC_DEFUN(SMB_SUBSYSTEM,
 ])
 
 
-dnl SMB_LIBRARY(name)
+dnl SMB_LIBRARY(name, default)
 dnl
 dnl configure build and use of an (internal) shared library
 dnl
@@ -81,6 +81,32 @@ AC_SUBST([INSTALL_]LIBUC)
 AC_SUBST([UNINSTALL_]LIBUC)
 
 AC_MSG_CHECKING([whether to build the LIBNAME shared library])
+m4_if([$2], [no], [
+dnl set the default to not build the shared lib
+AC_ARG_WITH(LIBNAME,
+AS_HELP_STRING([--with-]LIBNAME,
+	m4_if([$3], [],
+		[Build the LIBNAME shared library (default=no)],
+		[Build the LIBNAME shared library (default=no ($3))])),
+[
+case "$withval" in
+	yes)
+		build_lib=yes
+		;;
+	*)
+		AC_MSG_RESULT(yes)
+		build_lib=no
+		;;
+esac
+],
+[
+# if unspecified, default is not to build
+AC_MSG_RESULT(yes)
+build_lib=no
+]
+)
+],[
+dnl by default, try to build the shared lib
 AC_ARG_WITH(LIBNAME,
 AS_HELP_STRING([--with-]LIBNAME,
 	[Build the LIBNAME shared library (default=yes if shared libs supported)]),
@@ -100,6 +126,7 @@ esac
 build_lib=yes
 ]
 )
+])
 
 if eval test x"$build_lib" = "xyes" ; then
 	# only set the install targets if the user chose the library