fixed build for gcc 11

Xcoin.c

@@ -33,7 +33,7 @@ typedef struct {
 	sph_echo512_context		echo1;
 } Xhash_context_holder;
 
-Xhash_context_holder base_contexts;
+static Xhash_context_holder base_contexts;
 
 void init_Xhash_contexts()
 {

quark.c

@@ -22,7 +22,7 @@ typedef struct {
 	sph_keccak512_context	keccak1, keccak2;
 } quarkhash_context_holder;
 
-quarkhash_context_holder base_contexts;
+static quarkhash_context_holder base_contexts;
 
 void init_quarkhash_contexts()
 {
@@ -249,4 +249,4 @@ int scanhash_quark(int thr_id, uint32_t *pdata, const uint32_t *ptarget,
 	*hashes_done = n - first_nonce + 1;
 	pdata[19] = n;
 	return 0;
-}
+}