Stop IBCMerge for VSSetup project (#3611)
Stop IBCMerge for VSSetup project (#3611)

src\Package\MSBuild.VSSetup\MSBuild.VSSetup.csproj has an assembly name
that matches a shipped assembly, so the IBCMerge targets attempt to
apply PGO data to it, but it does not have any matching methods because
it's not a real project.

Respect the preexisting `$(MicroBuild_EnablePGO)` when deciding whether
to include the IBCMerge targets.
Microsoft/msbuild,mono/msbuild,sean-gilliam/msbuild,sean-gilliam/msbuild,cdmihai/msbuild,AndyGerlicher/msbuild,mono/msbuild,rainersigwald/msbuild,rainersigwald/msbuild,jeffkl/msbuild,chipitsine/msbuild,cdmihai/msbuild,chipitsine/msbuild,rainersigwald/msbuild,cdmihai/msbuild,mono/msbuild,chipitsine/msbuild,jeffkl/msbuild,cdmihai/msbuild,mono/msbuild,AndyGerlicher/msbuild,AndyGerlicher/msbuild,chipitsine/msbuild,jeffkl/msbuild,jeffkl/msbuild,Microsoft/msbuild,sean-gilliam/msbuild,sean-gilliam/msbuild,Microsoft/msbuild,Microsoft/msbuild,AndyGerlicher/msbuild,rainersigwald/msbuild