Building PowerShell when it complains about win10-x86 not being a valid value for a variable

Today I tried to compile the official PowerShell repository, but received an error that started with this:

"The variable cannot be validated because the value is not a valid value for the Runtime variable."

win10-x86 is apparently not one of the supported runtimes for the full-CLR version of PowerShell. I have 64-bit Windows 10, but the Git Shell always ran 32-bit PowerShell. It's possible that the 32-bitness of the calling program caused the dotnet utility to return the x86 version of the OS, but I'm not sure. Anyway, I ended up manually modifying build.psm1 to simply set $Runtime to win10-x64 on line 530, as opposed to running dotnet. Then the official instructions worked as expected.