Add support for *.manifest source files with MSVC tools

Classify .manifest sources separately, add dependencies on them, and
pass them to the MS manifest tool to merge with linker-generated
manifest files.

Inspired-by: Gilles Khouzam <gillesk@microsoft.com>

Source/cmLocalGenerator.h

@@ -219,6 +219,7 @@ public:
     const char* TargetSOName;
     const char* TargetInstallNameDir;
     const char* LinkFlags;
+    const char* Manifests;
     const char* LanguageCompileFlags;
     const char* Defines;
     const char* Includes;