Revert pull request #2637 to fix git-head regression issue 13498

https://issues.dlang.org/show_bug.cgi?id=13498

This reverts commit 875f2fe0314931ef86e597a3d87069c1b914c5bb, reversing
changes made to f5c7e97f2b4ee12e5e486da130ebf69483693bc5.

The changed absolutePath code essentially cannot work because the buildPath() result is not implicitly convertible to inout(char)[], but it was accidentally accepted by the regression 13498.