macOS: Restore support for Mac OS X 10.4 (Tiger)

Since commit 4aed96e230 (Apple: Set CMAKE_SHARED_LIBRARY_RUNTIME_C_FLAG
on non-macOS too, 2021-04-06, v3.20.1~5^2) we always enable support for
linking with `-rpath`.  The intention of the change was to enable using
the flag on iOS, tvOS and watchOS by avoiding a Darwin-specific version
check.  However, removing the check broke support for OS X 10.4 because
the flag is not supported on that version.

Restore a form of the check that disables the flag on OS X < 10.5 while
still allowing it for the other Apple platforms.  Since no one is doing
iOS/tvOS/etc development on 10.4, this change should have no unintended
side effects.

Fixes: #22490

Modules/Platform/Darwin.cmake

@@ -47,7 +47,9 @@ set(CMAKE_SHARED_MODULE_PREFIX "lib")
 set(CMAKE_SHARED_MODULE_SUFFIX ".so")
 set(CMAKE_MODULE_EXISTS 1)
 set(CMAKE_DL_LIBS "")
-set(CMAKE_SHARED_LIBRARY_RUNTIME_C_FLAG "-Wl,-rpath,")
+if(NOT "${_CURRENT_OSX_VERSION}" VERSION_LESS "10.5")
+  set(CMAKE_SHARED_LIBRARY_RUNTIME_C_FLAG "-Wl,-rpath,")
+endif()
 
 foreach(lang C CXX OBJC OBJCXX)
   set(CMAKE_${lang}_OSX_COMPATIBILITY_VERSION_FLAG "-compatibility_version ")