ld bootstrap test in build dir with path containing symlinks

This allows the bootstrap test to run if you have a symlink somewhere
in the build path directory.  $ld depends on $base_dir which is set
via tcl [pwd], collapsing the symlink like /usr/bin/pwd, while $objdir
contains the symlink.

	* testsuite/ld-bootstrap/bootstrap.exp: Normalize paths when
	checking for ld build directory.