Fix of warnings on aarch64 like:

bson.cpp:1775:3: error: case label value is less than minimum value for type [-Werror]
   case TYPE_NULL:
bson.cpp:1776:7: error: statement will never be executed [-Werror=switch-unreachable]
     b = true;

storage/connect/bson.cpp

@@ -767,7 +767,7 @@ bool BDOC::SerializeValue(PBVAL jvp, bool b)
   case TYPE_DBL:
     sprintf(buf, "%.*lf", jvp->Nd, *(double*)MakePtr(Base, jvp->To_Val));
     return jp->WriteStr(buf);
-  case TYPE_NULL:
+  case (char)TYPE_NULL:
     return jp->WriteStr("null");
   case TYPE_JVAL:
     return SerializeValue(MVP(jvp->To_Val));
@@ -1557,7 +1557,7 @@ PSZ BJSON::GetString(PBVAL vp, char* buff)
   case TYPE_BOOL:
     p = (PSZ)((vlp->B) ? "true" : "false");
     break;
-  case TYPE_NULL:
+  case (char)TYPE_NULL:
     p = (PSZ)"null";
     break;
   default:
@@ -1772,7 +1772,7 @@ bool BJSON::IsValueNull(PBVAL vlp)
   bool b;
 
   switch (vlp->Type) {
-  case TYPE_NULL:
+  case (char)TYPE_NULL:
     b = true;
     break;
   case TYPE_JOB:

storage/connect/bsonudf.cpp

@@ -491,7 +491,7 @@ void BJNX::SetJsonValue(PGLOBAL g, PVAL vp, PBVAL vlp)
 		case TYPE_JOB:
 			vp->SetValue_psz(GetObjectText(g, vlp, NULL));
 			break;
-		case TYPE_NULL:
+		case (char)TYPE_NULL:
 			vp->SetNull(true);
 		default:
 			vp->Reset();
@@ -1320,7 +1320,7 @@ my_bool BJNX::CompareValues(PGLOBAL g, PBVAL v1, PBVAL v2)
 				b = (v1->B == v2->B);
 
 			break;
-		case TYPE_NULL:
+		case (char)TYPE_NULL:
 			b = (v2->Type == TYPE_NULL);
 			break;
 		default: