MSBUILD / csc: Cleanest way of handling x64 mscorlib warning 1607

I found by changing my project's Target framework to .NET Framework 4 it eliminated the warning.

In this blog I found a proposal that is too long to copy it entirely over here, but in short the idea can be described with summary adapted from this comment:

In the project file, you can define a custom variable in the PropertyGroup section for each build configuration. Example:

<PropertyGroup Condition="'$(Configuration)|$(Platform)' == 'Release|x64'">
    <MyCustomPath>C:\Windows\Microsoft.NET\Framework64</MyCustomPath>
</PropertyGroup>

Just add a tag such as

<Reference Include="System.Data">
    <HintPath>$(MyCustomPath)</HintPath> 
</Reference>

and then use the macro to define the reference path. You can define MyCustomPath to a different location for different build configurations (platform and/or debug/release).
The problem would not exist if MS would support this in the VS UI, but until then this will work. I use this technique to reference different versions of the same assemblies in my debug & release builds. Works great!

In the above recitation I recovered the tag that was lost in the source commentarium and changed the wording to be somewhat more detailed.

An additional interesting piece from the same blog:

There’s some other ways to do this but they also require one to manually edit the project files. One way is to specify conditions to PropertyGroup-sections. This StackOverflow question highlights the use of conditions.