[Minor] Fix some compiler warnings

CMakeLists.txt

 
 PROJECT(rspamd VERSION "${RSPAMD_VERSION}" LANGUAGES C CXX ASM)
 
+CMAKE_POLICY(SET CMP0075 NEW)
+
 # This is supported merely with cmake 3.1
 SET(CMAKE_C_STANDARD 11)
 SET(CMAKE_C_STANDARD_REQUIRED ON)

contrib/mumhash/mum.h

      multiplication.  If we use a generic code we actually call a
      function doing 128x128->128 bit multiplication.  The function is
      very slow.  */
-  lo = v * p, hi;
+  lo = v * p;
   __asm__ ("umulh %0, %1, %2" : "=r" (hi) : "r" (v), "r" (p));
 #else
   __uint128_t r = (__uint128_t) v * (__uint128_t) p;

src/fuzzy_storage.c

 rspamd_fuzzy_check_callback (struct rspamd_fuzzy_reply *result, void *ud)
 {
 	struct fuzzy_session *session = ud;
-	gboolean encrypted = FALSE, is_shingle = FALSE;
+	gboolean is_shingle = FALSE, __attribute__ ((unused)) encrypted = FALSE;
 	struct rspamd_fuzzy_cmd *cmd = NULL;
 	const struct rspamd_shingle *shingle = NULL;
 	struct rspamd_shingle sgl_cpy;
 static void
 rspamd_fuzzy_process_command (struct fuzzy_session *session)
 {
-	gboolean encrypted = FALSE, is_shingle = FALSE;
+	gboolean is_shingle = FALSE, __attribute__ ((unused)) encrypted = FALSE;
 	struct rspamd_fuzzy_cmd *cmd = NULL;
 	struct rspamd_fuzzy_reply result;
 	struct fuzzy_peer_cmd up_cmd;

src/libcryptobox/cryptobox.c

 static void
 rspamd_cryptobox_cpuid (gint cpu[4], gint info)
 {
-	guint32 eax, ecx = 0, ebx = 0, edx = 0;
+	guint32 __attribute__ ((unused)) eax, __attribute__ ((unused)) ecx = 0, __attribute__ ((unused)) ebx = 0, __attribute__ ((unused)) edx = 0;
 
 	eax = info;
 #if defined(__GNUC__) && (defined(__x86_64__) || defined(__i386__))

src/libserver/re_cache.c

 {
 	lua_State *L = (lua_State *)task->cfg->lua_state;
 	GError *err = NULL;
-	struct rspamd_lua_text *t;
+	struct rspamd_lua_text __attribute__ ((unused)) *t;
 	gint text_pos;
 
 	if (G_LIKELY (lua_cbref == -1)) {

src/rspamd.c

 mark_old_workers (gpointer key, gpointer value, gpointer unused)
 {
 	struct rspamd_worker *w = value;
-	struct rspamd_main *rspamd_main;
+	struct rspamd_main __attribute__ ((unused)) *rspamd_main;
 
 	rspamd_main = w->srv;