Added the dxdiag.h header.

include/Makefile.in

diff --git a/include/Makefile.in b/include/Makefile.in
index 5b02e69..770ebb9 100644
--- a/include/Makefile.in
+++ b/include/Makefile.in
@@ -88,6 +88,7 @@
 	dsdriver.h \
 	dshow.h \
 	dsound.h \
+	dxdiag.h \
 	dxerr8.h \
 	dxerr9.h \
 	evcode.h \