m4/mpd_depends.m4: print warning when disabling the feature

configure.ac

@@ -552,7 +552,7 @@ dnl -------------------------------- libmpdclient ------------------------------
 MPD_ENABLE_AUTO_PKG_DEPENDS(libmpdclient, LIBMPDCLIENT,
 	[libmpdclient >= 2.2],
 	[MPD client library], [libmpdclient not found], [],
-	[enable_database], [Cannot use --enable-libmpdclient with --disable-database])
+	[enable_database], [Database support is disabled])
 
 dnl -------------------------------- expat --------------------------------
 MPD_ENABLE_AUTO_PKG(expat, EXPAT, [expat],
@@ -807,7 +807,7 @@ fi
 
 MPD_ENABLE_AUTO_PKG_DEPENDS(upnp, UPNP, [libupnp],
 	[UPnP client support], [libupnp not found], [],
-	[enable_database], [Cannot use --enable-upnp with --disable-database])
+	[enable_database], [Database support is disabled])
 
 dnl --------------------------------- libzzip ---------------------------------
 MPD_ENABLE_AUTO_PKG(zzip, ZZIP, [zziplib >= 0.13],

m4/mpd_auto.m4

@@ -181,5 +181,5 @@ dnl
 dnl Parameters: varname1, varname2, pkg, description, errmsg, default, dep_variable, dep_errmsg
 AC_DEFUN([MPD_ENABLE_AUTO_PKG_DEPENDS], [
 	MPD_ENABLE_AUTO_PKG([$1], [$2], [$3], [$4], [$5], [$6],
-		[MPD_DEPENDS([enable_$1], [$7], [$8])])
+		[MPD_DEPENDS([enable_$1], [$7], [$4], [$8])])
 ])

m4/mpd_depends.m4

@@ -2,13 +2,14 @@ dnl Declare a dependency of one feature on another.  If the depending
 dnl feature is disabled, the former must be disabled as well.  If the
 dnl former was explicitly enabled, abort with an error message.
 dnl
-dnl Parameters: varname1, varname2 (=dependency), errmsg
+dnl Parameters: varname1, varname2 (=dependency), description, errmsg
 AC_DEFUN([MPD_DEPENDS], [
 	if test x$$2 = xno; then
 		if test x$$1 = xauto; then
+			AC_MSG_WARN([$4: disabling $3])
 			$1=no
 		elif test x$$1 = xyes; then
-			AC_MSG_ERROR([$3])
+			AC_MSG_ERROR([$3: $4])
 		fi
 	fi
 ])