Merge topic 'msys_docs'

ec027aa6

 Help: Add documentation for MSYS variable
Acked-by: Kitware Robot <kwrobot@kitware.com>
Merge-request: !2882

Help/manual/cmake-variables.7.rst

@@ -276,6 +276,7 @@ Variables that Describe the System
    /variable/MSVC_IDE
    /variable/MSVC_TOOLSET_VERSION
    /variable/MSVC_VERSION
+   /variable/MSYS
    /variable/UNIX
    /variable/WIN32
    /variable/WINCE

Help/variable/MSYS.rst

+MSYS
+----
+
+``True`` when using the :generator:`MSYS Makefiles` generator.