Avoids "error: undefined symbol: posix_fadvise" if ANDROID_API_LEVEL is less than 21.

--- src/fccache.c
+++ src/fccache.c
@@ -962,7 +962,7 @@
     {
 #if defined(HAVE_MMAP) || defined(__CYGWIN__)
 	cache = mmap (0, fd_stat->st_size, PROT_READ, MAP_SHARED, fd, 0);
-#if defined(HAVE_POSIX_FADVISE) && defined(POSIX_FADV_WILLNEED)
+#if defined(HAVE_POSIX_FADVISE) && defined(POSIX_FADV_WILLNEED) && (!defined(__ANDROID_API__) || (__ANDROID_API__ >= 21))
 	posix_fadvise (fd, 0, fd_stat->st_size, POSIX_FADV_WILLNEED);
 #endif
 	if (cache == MAP_FAILED)