This is going to be very system-specific, because drive letters, install locations, and VS versions all vary. In fact this path doesn't work on my primary system, which has VS2010.

But fortunately MozillaBuild provides abstractions for accessing the batch script to which this link points, which is ultimately vcvars32.bat (the link points to vcvarsall.bat, which selects an architecture-specific batch script to invoke, and I can't say for sure on VS2012, but the equivalent link on my system points to the 32-bit script).

Indeed, MozillaBuild adds the relevant directories to *PATH*, so we should be able to invoke vcvars32.bat without having to specify the complete path.