scons: Collapse symlinks when installing git hooks.

When naively computing the relative path between the git hooks directory and a
hook we want to install, that will generally start with a few ".." path
components to work back out of the .git directory into the working directory.'
If the hooks directory is actually a symlink, then following ".." directory
entries won't get us back to where we came from, they'll take us to the actual
parent directory of hooks. The relative path we computed would then try to go
forward from this other directory using a path that would have worked in the
working directory, hopefully going somewhere that doesn't exist, but
potentially going to a totally unrelated file with the same relative path.

To avoid this problem, we should expand any symlinks in both the hooks
directory path, and the path to the hook script. That way, any ".." components
will go where we'd expect them to, and the relative path will actually go from
hooks to the script we expect.

Change-Id: I64d51bc817351f89b1d60eceaf450cc0a4553415
Reviewed-on: https://gem5-review.googlesource.com/2542
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>

SConstruct

@@ -407,8 +407,8 @@ def install_git_style_hooks():
         # and the hooks directory is not a symlink to an absolute path.
         if hook.is_under(main.root) and not abs_symlink_hooks:
             script_path = os.path.relpath(
-                script.get_abspath(),
-                hook.Dir(".").get_abspath())
+                os.path.realpath(script.get_abspath()),
+                os.path.realpath(hook.Dir(".").get_abspath()))
         else:
             script_path = script.get_abspath()