fuzz: Fix build for broken json-c repo

Current json-c master branch cannot be compiled with clang,
until upstream merges the fix, use the last stable branch
for fuzzers build.

Author: mbroz

tests/fuzz/oss-fuzz-build.sh

@@ -56,7 +56,8 @@ last_commit zlib
 [ ! -d xz ] && git clone -q --depth 1 https://github.com/tukaani-project/xz
 last_commit xz
 
-[ ! -d json-c ] && git clone -q --depth 1 https://github.com/json-c/json-c.git
+# Master branch is broken, use json-c-0.18 for now
+[ ! -d json-c ] && git clone -q --depth 1 --branch json-c-0.18 https://github.com/json-c/json-c.git
 last_commit json-c
 
 [ ! -d lvm2 ] && git clone -q --depth 1 https://gitlab.com/lvmteam/lvm2