Rework libpng Auxiliary support to address numerous problems (#636)

Auxiliary/DirectXTexPNG.h

@@ -18,16 +18,51 @@
 
 namespace DirectX
 {
+    enum PNG_FLAGS : uint32_t
+    {
+        PNG_FLAGS_NONE = 0x0,
+
+        PNG_FLAGS_BGR = 0x1,
+        // 24bpp files are returned as BGRX; 32bpp files are returned as BGRA
+
+        PNG_FLAGS_IGNORE_SRGB = 0x2,
+        // Ignores sRGB rendering intent
+
+        PNG_FLAGS_DEFAULT_LINEAR = 0x4,
+        // If no gamma or intent is specified assume linear
+
+        PNG_FLAGS_FORCE_SRGB = 0x20,
+        // Writes sRGB metadata into the file reguardless of format
+
+        PNG_FLAGS_FORCE_LINEAR = 0x40,
+        // Writes linear gamma metadata into the file reguardless of format
+    };
+
     DIRECTX_TEX_API HRESULT __cdecl GetMetadataFromPNGFile(
         _In_z_ const wchar_t* szFile,
+        PNG_FLAGS flags,
         _Out_ TexMetadata& metadata);
 
     DIRECTX_TEX_API HRESULT __cdecl LoadFromPNGFile(
         _In_z_ const wchar_t* szFile,
+        PNG_FLAGS flags,
         _Out_opt_ TexMetadata* metadata,
         _Out_ ScratchImage& image);
 
     DIRECTX_TEX_API HRESULT __cdecl SaveToPNGFile(
         _In_ const Image& image,
+        PNG_FLAGS flags,
         _In_z_ const wchar_t* szFile);
+
+#ifdef __clang__
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wdeprecated-dynamic-exception-spec"
+#pragma clang diagnostic ignored "-Wextra-semi-stmt"
+#endif
+
+DEFINE_ENUM_FLAG_OPERATORS(PNG_FLAGS);
+
+#ifdef __clang__
+#pragma clang diagnostic pop
+#endif
 }