Add uninstall target (AcademySoftwareFoundation#1624)

* Add uninstall target

Satisfy the OpenSSF Best Practices Badge requirement for an
insta/uninstall process:
https://www.bestpractices.dev/en/criteria/1#1.installation_common

CMake does not support a standard "uninstall" target, but the
community recommends implementing an "uninstal" target that remove files named in the
`install_manifest.txt`:
https://gitlab.kitware.com/cmake/community/-/wikis/FAQ#can-i-do-make-uninstall-with-cmake

However, our existing process of installing the symlink to the "bare"
library, i.e. the symlink from libImath-3_2.so to libImath.so, fails
to add the symlink to the manifest, so "make uninstall" misses the
symlink. The existing mechanism use "install(CODE execute_process(cmake -E create_symlink))".

This changes that to use a simpler "file(CREATE_LINK)" and
"install(FILES)" to accomplish the same thing while also registering
the symlink the the manifest.

Also, this fixes an issue where `OpenEXRConfig.h` was passed to
`install()` twice, producing two entries in `install_manifest.txt`.

Signed-off-by: Cary Phillips <[email protected]>

* mention uninstall in install instructions

Signed-off-by: Cary Phillips <[email protected]>

* poke

Signed-off-by: Cary Phillips <[email protected]>

* COPY_ON_ERROR

Signed-off-by: Cary Phillips <[email protected]>

* clarify the uninstall instructions

Signed-off-by: Cary Phillips <[email protected]>

---------

Signed-off-by: Cary Phillips <[email protected]>

CMakeLists.txt

@@ -59,6 +59,16 @@ if(NOT TARGET uninstall)
     COMMAND ${CMAKE_COMMAND} -P ${CMAKE_CURRENT_BINARY_DIR}/cmake_uninstall.cmake)
 endif()
 
+# uninstall target
+if(NOT TARGET uninstall)
+  configure_file(
+    "${CMAKE_CURRENT_SOURCE_DIR}/cmake/cmake_uninstall.cmake.in"
+    "${CMAKE_CURRENT_BINARY_DIR}/cmake_uninstall.cmake"
+    IMMEDIATE @ONLY)
+  add_custom_target(uninstall
+    COMMAND ${CMAKE_COMMAND} -P ${CMAKE_CURRENT_BINARY_DIR}/cmake_uninstall.cmake)
+endif()
+
 include(cmake/LibraryDefine.cmake)
 include(cmake/OpenEXRSetup.cmake)
 add_subdirectory(cmake)