Stub implementation of the dmusic dll.

diff --git a/configure.ac b/configure.ac
index 2cce51b..e7eb162 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1410,6 +1410,7 @@
 dlls/devenum/Makefile
 dlls/dinput/Makefile
 dlls/dinput8/Makefile
+dlls/dmusic/Makefile
 dlls/dplay/Makefile
 dlls/dplayx/Makefile
 dlls/dsound/Makefile