fuzzing REFACTOR fuzz harneses (#1126)

Fix minor issues with implicit function declarations, terminate fuzzer
string inputs with string termination characters and add an XML parser
harness
diff --git a/tests/fuzz/lyd_parse_mem.c b/tests/fuzz/lyd_parse_mem.c
new file mode 100644
index 0000000..75cbc93
--- /dev/null
+++ b/tests/fuzz/lyd_parse_mem.c
@@ -0,0 +1,82 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdbool.h>
+
+#include "libyang.h"
+
+int LLVMFuzzerTestOneInput(uint8_t const *buf, size_t len)
+{
+	struct ly_ctx *ctx = NULL;
+	static bool log = false;
+	const char *schema_a = "module defs {namespace urn:tests:defs;prefix d;yang-version 1.1;"
+		            "identity crypto-alg; identity interface-type; identity ethernet {base interface-type;} identity fast-ethernet {base ethernet;}}";
+    const char *schema_b = "module types {namespace urn:tests:types;prefix t;yang-version 1.1; import defs {prefix defs;}"
+            "feature f; identity gigabit-ethernet { base defs:ethernet;}"
+            "container cont {leaf leaftarget {type empty;}"
+                            "list listtarget {key id; max-elements 5;leaf id {type uint8;} leaf value {type string;}}"
+                            "leaf-list leaflisttarget {type uint8; max-elements 5;}}"
+            "list list {key id; leaf id {type string;} leaf value {type string;} leaf-list targets {type string;}}"
+            "list list2 {key \"id value\"; leaf id {type string;} leaf value {type string;}}"
+            "list list_inst {key id; leaf id {type instance-identifier {require-instance true;}} leaf value {type string;}}"
+            "list list_ident {key id; leaf id {type identityref {base defs:interface-type;}} leaf value {type string;}}"
+            "leaf-list leaflisttarget {type string;}"
+            "leaf binary {type binary {length 5 {error-message \"This base64 value must be of length 5.\";}}}"
+            "leaf binary-norestr {type binary;}"
+            "leaf int8 {type int8 {range 10..20;}}"
+            "leaf uint8 {type uint8 {range 150..200;}}"
+            "leaf int16 {type int16 {range -20..-10;}}"
+            "leaf uint16 {type uint16 {range 150..200;}}"
+            "leaf int32 {type int32;}"
+            "leaf uint32 {type uint32;}"
+            "leaf int64 {type int64;}"
+            "leaf uint64 {type uint64;}"
+            "leaf bits {type bits {bit zero; bit one {if-feature f;} bit two;}}"
+            "leaf enums {type enumeration {enum white; enum yellow {if-feature f;}}}"
+            "leaf dec64 {type decimal64 {fraction-digits 1; range 1.5..10;}}"
+            "leaf dec64-norestr {type decimal64 {fraction-digits 18;}}"
+            "leaf str {type string {length 8..10; pattern '[a-z ]*';}}"
+            "leaf str-norestr {type string;}"
+            "leaf str-utf8 {type string{length 2..5; pattern '€*';}}"
+            "leaf bool {type boolean;}"
+            "leaf empty {type empty;}"
+            "leaf ident {type identityref {base defs:interface-type;}}"
+ 	    "leaf inst {type instance-identifier {require-instance true;}}"
+            "leaf inst-noreq {type instance-identifier {require-instance false;}}"
+            "leaf lref {type leafref {path /leaflisttarget; require-instance true;}}"
+            "leaf lref2 {type leafref {path \"../list[id = current()/../str-norestr]/targets\"; require-instance true;}}"
+            "leaf un1 {type union {"
+            "type leafref {path /int8; require-instance true;}"
+            "type union { type identityref {base defs:interface-type;} type instance-identifier {require-instance true;} }"
+            "type string {length 1..20;}}}}";
+    	char *data = NULL;
+
+	LY_ERR err;
+
+	if (!log) {
+		ly_log_options(0);
+		log = true;
+	}
+
+	err = ly_ctx_new(NULL, 0, &ctx);
+	if (err != LY_SUCCESS) {
+		fprintf(stderr, "Failed to create context\n");
+		exit(EXIT_FAILURE);
+	}
+
+	lys_parse_mem(ctx, schema_a, LYS_IN_YANG);
+	lys_parse_mem(ctx, schema_b, LYS_IN_YANG);
+
+	data = malloc(len + 1);
+	if (data == NULL) {
+		return 0;
+	}
+	memcpy(data, buf, len);
+	data[len] = 0;
+
+	lyd_parse_mem(ctx, data, LYD_XML, LYD_VALOPT_DATA_ONLY);
+	ly_ctx_destroy(ctx, NULL);
+
+	free(data);
+
+	return 0;
+}