Fix more build errors in mingw

Based on #77

Author: sawickiap

src/D3D12MemAlloc.cpp

@@ -33,11 +33,24 @@
     #include <shared_mutex>
 #endif
 
-// Includes needed for MinGW - see #71.
-#ifndef _MSC_VER
-    #include <guiddef.h>
-    // guiddef.h must be included first.
-    #include <dxguids.h>
+// On older mingw versions, using the Agility SDK will cause linker errors unless dxguids.h is included.
+// But on newer mingw versions, the includes aren't necessary thus no need to grab DirectX-Headers.
+// Release cycles are slow for LTS distros on Linux, so this codeblock will need to stay for a few years.
+#if defined(__MINGW64_VERSION_MAJOR) && defined(__MINGW64_VERSION_MINOR) && \
+	defined(__MINGW64_VERSION_BUGFIX) && defined(__ID3D12Device8_INTERFACE_DEFINED__)
+    #define D3D12MA_MAKE_MINGW_VERSION(x, y, z) ((x << 20u) | (y << 10u) | (z))
+    #if D3D12MA_MAKE_MINGW_VERSION(__MINGW64_VERSION_MAJOR, __MINGW64_VERSION_MINOR, \
+								  __MINGW64_VERSION_BUGFIX) <= D3D12MA_MAKE_MINGW_VERSION(11, 0, 1)
+        #if defined(__has_include)
+            #if !__has_include(<dxguids.h>)
+                #error "mingw or gcc detected. dxguids.h is needed. You can grab it from https://github.com/microsoft/DirectX-Headers or if you're on Ubuntu just run sudo apt install directx-headers-dev"
+            #endif
+        #endif
+        #include <guiddef.h>
+        // // guiddef.h must be included first.
+        #include <dxguids.h>
+    #endif
+    #undef D3D12MA_MAKE_MINGW_VERSION
 #endif
 
 ////////////////////////////////////////////////////////////////////////////////