If you've tried to build an OpenMP application and seen this error dialog pop-up: "This application has failed to start because vcompd.dll was not found." then you've come to the right place.
It turns out that due to vcomp(d).lib being a pure import lib it doesn't have a manifest in it. So to get the manifest for vcomp(d).dll we put it in omp.h. In fact if you look in omp.h, starting with this line, #if !defined(_OPENMP_NOFORCE_MANIFEST), you will see where we do the manifest generation.
This requires the programmer to include omp.h even in cases where they're only using OpenMP pragmas. Should only be five seconds worth of work, although more than five seconds worth of work to figure out what the problem was. Hopefully this blog has all of the keywords one might search if they run across this issue.