[libxml2] Add options file for xml fuzzer

[Nick Wellnhofer <nwellnhof src gnome org>]

commit e98150d4444c931afa6b28f50b6ac667a33defd8
Author: Nick Wellnhofer <wellnhofer aevum de>
Date:   Tue Jun 9 13:45:31 2020 +0200

    Add options file for xml fuzzer
    
    This will be picked up OSS-Fuzz, limiting the maximum input size to
    80 KB and hopefully avoiding timeouts. Some of the timeouts seem to be
    related to our suboptimal handling of excessive entity expansion.
    The new fuzzers support external entities and make this problem even
    more prominent.

 fuzz/xml.options | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/fuzz/xml.options b/fuzz/xml.options
new file mode 100644
index 00000000..09f13d89
--- /dev/null
+++ b/fuzz/xml.options
@@ -0,0 +1,2 @@
+[libfuzzer]
+max_len = 80000