contrib: d3d9: Support prefix out of the contrib directory

contrib/src/d3d9/dxva2api.patch

---- ../tarballs/dxva2api.idl	2017-06-13 14:45:14.598269100 +0200
-+++ dxva2api/dxva2api.idl	2017-06-26 10:08:58.732675300 +0200
+--- a/dxva2api/dxva2api.idl	2017-06-13 14:45:14.598269100 +0200
++++ b/dxva2api/dxva2api.idl	2017-06-26 10:08:58.732675300 +0200
 @@ -6,6 +6,8 @@
  
  import "unknwn.idl";

contrib/src/d3d9/rules.mak

@@ -36,19 +36,20 @@ $(TARBALLS)/dxva2api.idl:
 
 $(DST_D3D9CAPS_H): $(TARBALLS)/d3d9caps.h .sum-d3d9
 	mkdir -p -- "$(PREFIX)/include/"
-	cp $(TARBALLS)/d3d9caps.h $@ && cd "$(PREFIX)/include/" && patch -fp1 < ../$(SRC)/d3d9/d3d9caps.patch
+	cd $(TARBALLS) && patch -fp1 < $(SRC)/d3d9/d3d9caps.patch -o $@
 
 $(DST_D3D9_H): $(TARBALLS)/d3d9.h .sum-d3d9
 	mkdir -p -- "$(PREFIX)/include/"
-	cp $(TARBALLS)/d3d9.h $@ && cd "$(PREFIX)/include/" && patch -fp1 < ../$(SRC)/d3d9/d3d9.patch
+	cd $(TARBALLS) && patch -fp1 < $(SRC)/d3d9/d3d9.patch -o $@
 
-dxva2api: .sum-d3d9
-	mkdir -p $@
-	cp $(TARBALLS)/dxva2api.idl $@ && cd $@ && patch -fp1 < ../$(SRC)/d3d9/dxva2api.patch
+dxva2api/dxva2api.idl: .sum-d3d9
+	mkdir -p dxva2api
+	cp $(TARBALLS)/dxva2api.idl $@
+	patch -fp1 < $(SRC)/d3d9/dxva2api.patch
 
-$(DST_DXVA2API_H): dxva2api
+$(DST_DXVA2API_H): dxva2api/dxva2api.idl
 	mkdir -p -- "$(PREFIX)/include/"
-	$(WIDL) -DBOOL=WINBOOL -D_D3D9_H_ -D__C89_NAMELESS -I$(IDL_INC_PATH) -h -o $@ $</dxva2api.idl
+	$(WIDL) -DBOOL=WINBOOL -D_D3D9_H_ -D__C89_NAMELESS -I$(IDL_INC_PATH) -h -o $@ $<
 
 .d3d9caps: $(DST_D3D9CAPS_H)
 	touch $@