configure: fixes vda compilation issue.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

configure

@@ -2959,7 +2959,6 @@ check_func_headers windows.h MapViewOfFile
 check_func_headers windows.h VirtualAlloc
 
 check_header dlfcn.h
-check_header VideoDecodeAcceleration/VDADecoder.h
 check_header dxva2api.h -D_WIN32_WINNT=0x0600
 check_header libcrystalhd/libcrystalhd_if.h
 check_header malloc.h
@@ -2975,9 +2974,12 @@ check_header X11/extensions/XvMClib.h
 disabled  zlib || check_lib   zlib.h      zlibVersion -lz   || disable  zlib
 disabled bzlib || check_lib2 bzlib.h BZ2_bzlibVersion -lbz2 || disable bzlib
 
-# adds ldflags for VDA module
-if enabled vda; then
+# check for VDA header
+if ! disabled vda; then
+    if check_header VideoDecodeAcceleration/VDADecoder.h; then
+        enable vda
         add_ldflags -framework CoreFoundation -framework VideoDecodeAcceleration -framework QuartzCore
+    fi
 fi
 
 # check for some common methods of building with pthread support