Fixes build on arm64 (and other platforms with unsigned char).

https://github.com/xmrig/xmrig/commit/f4cdc527b00571150e8521331928c75b44e071f9.patch
https://github.com/xmrig/xmrig/issues/2527

From f4cdc527b00571150e8521331928c75b44e071f9 Mon Sep 17 00:00:00 2001
From: XMRig <support@xmrig.com>
Date: Tue, 10 Aug 2021 01:40:36 +0700
Subject: [PATCH] #2527 Fix narrowing conversion.

---
 src/base/net/stratum/DaemonClient.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/base/net/stratum/DaemonClient.cpp b/src/base/net/stratum/DaemonClient.cpp
index 77818f34c..76f30c653 100644
--- a/src/base/net/stratum/DaemonClient.cpp
+++ b/src/base/net/stratum/DaemonClient.cpp
@@ -65,7 +65,7 @@ static const char *kJsonRPC                 = "/json_rpc";
 
 static constexpr size_t kBlobReserveSize    = 8;
 
-static const char kZMQGreeting[64] = { -1, 0, 0, 0, 0, 0, 0, 0, 0, 127, 3, 0, 'N', 'U', 'L', 'L' };
+static const char kZMQGreeting[64] = { static_cast<char>(-1), 0, 0, 0, 0, 0, 0, 0, 0, 127, 3, 0, 'N', 'U', 'L', 'L' };
 static constexpr size_t kZMQGreetingSize1 = 11;
 
 static const char kZMQHandshake[] = "\4\x19\5READY\xbSocket-Type\0\0\0\3SUB";