Problem: msbuild uses timestamps to determine what needs to be rebuilt, and git doesn't track files' last modified time, so everything is always fully rebuilt.
Solution: This commit adds an sqlite database that tracks C/C++ files and their md5 hashes. If a file's hash hasn't changed, then it doesn't need to be rebuilt, so its last modified time is backdated 20 years. The 20 years is an arbitrarily chosen amount of time and has no special significance.
