Add amstream dll (MultiMedia Streams), part of Direct Show.

diff --git a/configure.ac b/configure.ac
index 935ae15..996a3d7 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1492,6 +1492,7 @@
 dlls/Makefile
 dlls/advapi32/Makefile
 dlls/advapi32/tests/Makefile
+dlls/amstream/Makefile
 dlls/avicap32/Makefile
 dlls/avifil32/Makefile
 dlls/cabinet/Makefile