#370 make: bugfix for gnu make $(abspath)

[Alexandre Girao]

abspath function does not work with native win32 paths, e.g.: c:/absolute/path

i made very simple changes and also simplified the algorithm just a bit.

note: there is no group for the make yet on gnuwin32 project.

[Alexandre Girao]

the patch for gnuwin32 make 3.81 source