Reflect the input file hash when building the library

[kekyo]

It should be implemented to speed up the build process.
All source code converted by IL2C is overwritten, so it is judged by hash value, not by timestamp.

• At present, the time required for conversion is negligible, and it is acceptable to convert everything every time.
• Judgment is made at compiler runtime to avoid unnecessary processing.
• Re-execute all compilation when headers (*.h) have been changed.
• Due to the above, MSBuild scripts cannot achieve this.