tools: Fix "lib" symlink created inside $(STAGING_DIR_HOST)/lib

tools: Fix "lib" symlink created inside $(STAGING_DIR_HOST)/lib

Currently, if "make tools/install" is called after tools have already
been installed, a symbolic link named "lib" will be created inside
$(STAGING_DIR_HOST)/lib, pointing to "lib" (i.e. itself).

During tools/prepare, a "lib64" symlink is created inside
$(STAGING_DIR_HOST) that points to "lib" (also inside
$(STAGING_DIR_HOST)).

If tools/prepare is called and the "lib64" symlink already exists, then
ln will treat it as a directory and instead create a symlink named "lib"
inside of that directory.

This adds the -n option for ln so that $(STAGING_DIR_HOST)/lib64 is
always treated as a normal file (the link name), not as a directory.

Signed-off-by: Jeffery To <jeffery.to@gmail.com>