install.sh: avoid creating symlinks with restricted permissions

Linux and most systems do not have symlink permissions, but some
systems, including MacOS, do, and creation of the symlink with umask
set to 0777 makes the symlink inaccessible on such systems.

clear umask when making a symlink so that the behavior is uniform.

tools/install.sh

@@ -48,7 +48,9 @@ trap 'rm -f "$tmp"' EXIT INT QUIT TERM HUP
 umask 077
 
 if test "$symlink" ; then
+umask 000
 ln -s "$1" "$tmp"
+umask 077
 else
 cat < "$1" > "$tmp"
 chmod "$mode" "$tmp"