Update vsproj search paths (libsdl-org/SDL#7139)

VisualC/SDL/SDL.vcxproj

@@ -86,16 +86,16 @@
     <LibraryPath Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'">C:\Program Files %28x86%29\Microsoft DirectX SDK %28June 2010%29\Lib\x86;$(LibraryPath)</LibraryPath>
   </PropertyGroup>
   <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'">
-    <IncludePath>$(SolutionDir)/../src;$(IncludePath)</IncludePath>
+    <IncludePath>$(ProjectDir)/../../src;$(IncludePath)</IncludePath>
   </PropertyGroup>
   <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Release|Win32'">
-    <IncludePath>$(SolutionDir)/../src;$(IncludePath)</IncludePath>
+    <IncludePath>$(ProjectDir)/../../src;$(IncludePath)</IncludePath>
   </PropertyGroup>
   <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|x64'">
-    <IncludePath>$(SolutionDir)/../src;$(IncludePath)</IncludePath>
+    <IncludePath>$(ProjectDir)/../../src;$(IncludePath)</IncludePath>
   </PropertyGroup>
   <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Release|x64'">
-    <IncludePath>$(SolutionDir)/../src;$(IncludePath)</IncludePath>
+    <IncludePath>$(ProjectDir)/../../src;$(IncludePath)</IncludePath>
   </PropertyGroup>
   <ItemDefinitionGroup Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'">
     <PreBuildEvent>