Replace local header placeholders in appinstaller with direct references to upstream headers. Deleted the gitlink/header stubs (certmgr.h, notice.h, pkgmgr.h, pkgread.h, priformatcli.h) from appinstaller, updated main.cpp and appxinfo.h to include the ../path to those headers, and adjusted appinstaller.vcxproj.filters to point to the new locations. Cleans up redundant local links and ensures the project references the original header files.
Upgrade solution to Visual Studio 17 and add ARM build configurations across projects. Several .vcxproj files were updated to include Debug/Release|ARM property groups, property sheet imports and LinkIncremental settings; platform toolset set for ARM configs where appropriate. A new pugixml_arm project and its sources/filters were added. Also added ExtensibilityGlobals (SolutionGuid) to the .sln.
