Cygwin: Apply patches from downstream CMake package

Lemures Lemniscatirequested to merge
lemniscati/cmake:cygwin-patches into master

Based on downstream patches from Cygwin package for CMake by Marco Atzeri.

  • Their changes are expected to be non-breaking for non-Cygwin environments.
  • References to the original patches are written in their commit messages respectively.
Edited by Brad King

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