major: Switch to forward slashes(+more) to fix compilation on Linux (#1403)

Notably also adds some metadata files for NixOS 

* add support for linux clang cross compiles

* add linux clang instructions

* un-capitalize Mob.horse.*

* update the description in flake.nix

---------

Co-authored-by: Loki <lokirautio@gmail.com>

Minecraft.Client/PS3/Network/SQRNetworkManager_PS3.cpp

@@ -15,9 +15,9 @@
 #include "SonyVoiceChat.h"
 #include "Common/Network/Sony/SonyHttp.h"
 #endif
-#include "..\..\..\Minecraft.World\C4JThread.h"
-#include "..\PS3Extras\PS3Strings.h"
-#include "PS3\Network\SonyRemoteStorage_PS3.h"
+#include "../../../Minecraft.World/C4JThread.h"
+#include "../PS3Extras/PS3Strings.h"
+#include "PS3/Network/SonyRemoteStorage_PS3.h"
 
 int (* SQRNetworkManager_PS3::s_SignInCompleteCallbackFn)(void *pParam, bool bContinue, int pad) = nullptr;
 void * SQRNetworkManager_PS3::s_SignInCompleteParam = nullptr;

Minecraft.Client/PS3/Network/SQRNetworkManager_PS3.h

@@ -9,7 +9,7 @@
 #endif
 #include <queue>
 
-#include "..\..\Common\Network\Sony\SQRNetworkManager.h"
+#include "../../Common/Network/Sony/SQRNetworkManager.h"
 
 class SQRNetworkPlayer;
 class ISQRNetworkManagerListener;

Minecraft.Client/PS3/Network/SonyCommerce_PS3.cpp

@@ -1,7 +1,7 @@
 #include "stdafx.h"
 
 #include "SonyCommerce_PS3.h"
-#include "..\PS3Extras\ShutdownManager.h"
+#include "../PS3Extras/ShutdownManager.h"
 #include <sys/event.h>
 
 

Minecraft.Client/PS3/Network/SonyCommerce_PS3.h

@@ -6,7 +6,7 @@
 #include <np.h>
 #include <np/drm.h>
 #include <np/commerce2.h>
-#include "Common\Network\Sony\SonyCommerce.h"
+#include "Common/Network/Sony/SonyCommerce.h"
 
 #define SCE_TOOLKIT_NP_SKU_PRICE_LEN	(SCE_NP_COMMERCE2_CURRENCY_CODE_LEN \
 	+ SCE_NP_COMMERCE2_CURRENCY_SYMBOL_LEN \

Minecraft.Client/PS3/Network/SonyRemoteStorage_PS3.h

@@ -1,7 +1,7 @@
 #pragma once 
 
 
-#include "Common\Network\Sony\sceRemoteStorage\header\sceRemoteStorage.h"
+#include "Common/Network/Sony/sceRemoteStorage/header/sceRemoteStorage.h"
 
 class SonyRemoteStorage_PS3 : public SonyRemoteStorage
 {