Import omake-0.9.8.5 as devel/omake.

Import omake-0.9.8.5 as devel/omake.
Based on PR#43374 by YAMAMOTO Takeshi, some improvements.

OMake is a build system, similar to GNU make, but with many additional
features, including:
- Support for large projects spanning multiple directories;
- Support for commands that produce several targets at once;
- Fast, accurate, automated dependency analysis using MD5 digests;
- Portability: omake provides a consistent interface on Win32
  and on Unix systems including Linux, OSX, and Cygwin;
- Builtin functions that provide the most common features of
  programs like grep, sed, and awk;
- Active filesystem monitoring, where the build automatically
  restarts whenever you modify a source file.