Fix to detect vsnprintf prototype properly

From the standard sepc, <stdio.h> is required in addition to <stdarg.h>

Signed-off-by: OBATA Akio <obache@wizdas.com>
(cherry picked from commit cc7cd83235)

CMakeLists.txt

@@ -343,7 +343,7 @@ check_symbol_exists( ffs       "string.h" HAVE_FFS_PROTO )
 check_symbol_exists( asprintf  "stdio.h"  HAVE_ASPRINTF_PROTO )
 check_symbol_exists( vasprintf "stdio.h"  HAVE_VASPRINTF_PROTO )
 check_symbol_exists( snprintf  "stdio.h"  HAVE_SNPRINTF_PROTO )
-check_symbol_exists( vsnprintf "stdarg.h" HAVE_VSNPRINTF_PROTO )
+check_symbol_exists( vsnprintf "stdarg.h;stdio.h" HAVE_VSNPRINTF_PROTO )
 check_symbol_exists( strvercmp "string.h" HAVE_STRVERCMP_PROTO )