Try to migrate yajl-ruby and libxslt to LIB_FUZZING_ENGINE (#2365)

projects/libxslt/build.sh

@@ -48,7 +48,7 @@ for fuzzer in xpath xslt; do
     $CXX $CXXFLAGS \
         tests/fuzz/$fuzzer.o \
         -o $OUT/$fuzzer \
-        -lFuzzingEngine \
+        $LIB_FUZZING_ENGINE \
         libexslt/.libs/libexslt.a libxslt/.libs/libxslt.a \
         ../libxml2/.libs/libxml2.a \
         $CRYPTO_LIBS

projects/yajl-ruby/build.sh

@@ -25,4 +25,4 @@ mv $SRC/*.dict $OUT/
 $CXX $CXXFLAGS -I. \
     -x c yajl.c yajl_alloc.c yajl_buf.c yajl_lex.c yajl_parser.c yajl_encode.c \
     ../../fuzz/json_fuzzer.c -o $OUT/json_fuzzer \
-    -lFuzzingEngine
+    $LIB_FUZZING_ENGINE