FindTclsh: Drop Cygwin-specific behavior and use POSIX code path
Based on downstream patch from Cygwin package for CMake by Marco Atzeri:
* https://github.com/matzeri/cygwin-pkg/blob/64864eb8f0d635ea44226e4b9a41a7ca59a1c7dd/cmake/3.17.3-findtclsh.patch
diff --git a/Modules/FindTclsh.cmake b/Modules/FindTclsh.cmake
index 82be473..f306d5b 100644
--- a/Modules/FindTclsh.cmake
+++ b/Modules/FindTclsh.cmake
@@ -15,15 +15,8 @@
TCLSH_FOUND = TRUE if tclsh has been found
TCL_TCLSH = the path to the tclsh executable
-
-In cygwin, look for the cygwin version first. Don't look for it later
-to avoid finding the cygwin version on a Win32 build.
#]=======================================================================]
-if(CYGWIN)
- find_program(TCL_TCLSH NAMES cygtclsh83 cygtclsh80)
-endif()
-
get_filename_component(TK_WISH_PATH "${TK_WISH}" PATH)
get_filename_component(TK_WISH_PATH_PARENT "${TK_WISH_PATH}" PATH)
string(REGEX REPLACE
