Core: Fix a -Wshadow warning in gcc 11

This moves the only direct call to zlib’s crc32() into its own
translation unit, but that operation is cold enough that this won’t
matter in the slightest.  crc32_z() would be more appropriate, but
Android has an older zlib version…

Source/Core/Common/CRC32.h

@@ -0,0 +1,11 @@
+// Copyright 2021 Dolphin Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include <string_view>
+
+#include "Common/CommonTypes.h"
+
+namespace Common
+{
+u32 ComputeCRC32(std::string_view data);
+}  // namespace Common