Merge branch 'backport-FindCygwin-fix-regression' into release-3.9

Merge-request: !1128

Modules/FindCygwin.cmake

@@ -8,14 +8,17 @@
 # this module looks for Cygwin
 
 if (WIN32)
-  find_program(CYGWIN_INSTALL_PATH
+  if(CYGWIN_INSTALL_PATH)
+    set(CYGWIN_BAT "${CYGWIN_INSTALL_PATH}/cygwin.bat")
+  endif()
+
+  find_program(CYGWIN_BAT
     cygwin.bat
     "C:/Cygwin"
     "[HKEY_LOCAL_MACHINE\\SOFTWARE\\Cygwin\\setup;rootdir]"
     "[HKEY_LOCAL_MACHINE\\SOFTWARE\\Cygnus Solutions\\Cygwin\\mounts v2\\/;native]"
   )
-  get_filename_component(CYGWIN_INSTALL_PATH "${CYGWIN_INSTALL_PATH}" DIRECTORY)
-  mark_as_advanced(
-    CYGWIN_INSTALL_PATH
-  )
+  get_filename_component(CYGWIN_INSTALL_PATH "${CYGWIN_BAT}" DIRECTORY)
+  mark_as_advanced(CYGWIN_BAT)
+
 endif ()