x265: detect X265_BUILD

As the library symbols are suffixed with the exact build version, and
it is not clear yet whether the API will be broken or simply extended,
watch for the exact version number (which is 1)

configure.ac

@@ -2725,8 +2725,13 @@ dnl x265 encoder
 AC_ARG_ENABLE(x265,
   AS_HELP_STRING([--enable-x265],[H265 / HEVC encoding support with libx265 (default enabled)]))
 AS_IF( [test "${enable_x265}" != "no"],[
-  AC_CHECK_HEADER([x265.h], [
-      AC_CHECK_LIB([x265],[x265_encoder_open], [
+  AC_PREPROC_IFELSE([AC_LANG_SOURCE([
+#include <x265.h>
+#if X265_BUILD != 1
+# error Fail
+#endif
+  ])], [
+    AC_CHECK_LIB([x265],[x265_encoder_open_1], [
       VLC_ADD_PLUGIN([x265])
       VLC_ADD_LIBS([x265], [-lx265 -lstdc++ -lm -lpthread])
     ], [