Enable multi-module for CoreCLR tests

[nattress]

• Allows runtest.cmd /multimodule /coreclr
• Modify build integration targets to allow for tests with multiple
  assemblies. We have two set of assembly inputs to ILC: @(ManagedLibrary)
  which despite being an Item contains the main managed assembly to use as
  the template name for the response file and output object file base
  name. @(IlcCompileInput) is the list of assemblies that are inputs to
  Ilc. This change allows us to compile all the app assemblies into a
  single object file.
• Specify the inputs / outputs to the MSBuild task that builds the
  framework assembly obj files. This removes a page of spam per test when
  MSBuild skips over the already-built obj files.
• Currently 12 tests fail due to some EH issue that needs investigating.

[MichalStrehovsky]

I think this is causing about 70 new failures in the rolling build:

          Unhandled Exception: System.InvalidOperationException: PE image does not have metadata.
             at System.Reflection.PortableExecutable.PEReader.GetMetadataBlock()
             at System.Reflection.Metadata.PEReaderExtensions.GetMetadataReader(PEReader peReader, MetadataReaderOptions options, MetadataStringDecoder utf8Decoder)
             at Internal.TypeSystem.Ecma.EcmaModule.CreateMetadataReader(TypeSystemContext context, PEReader peReader)
             at Internal.TypeSystem.Ecma.EcmaModule.Create(TypeSystemContext context, PEReader peReader, PdbSymbolReader pdbReader)
             at ILCompiler.CompilerTypeSystemContext.AddModule(String filePath, String expectedSimpleName)
             at ILCompiler.CompilerTypeSystemContext.GetModuleFromPath(String filePath)
             at ILCompiler.Program.Run(String[] args)

I assume it's because we allow passing all sorts of garbage as -r parameter, but are more sensitive about inputs. Some of the files this is passing as inputs are actually native DLL dependencies. I'm not sure there's a good way to go about this besides baselining this or hacking the compiler in the short term :/.

There are about 70 more failures in the rolling build due to a RyuJIT update. I'll have a closer look at them later in the week and file issues.