strict POSIX requires a path to specified to `find`

extra/scripts/install_headers.sh

@@ -33,7 +33,7 @@ fi
 (
 # We must cd, or else we'll prepend "$1" to filenames!
 cd "$1" || exit 1
-find ! -name '.' -a ! -path '*/.*' | sed -e 's/^\.\///' -e '/^config\//d' \
+find . ! -name '.' -a ! -path '*/.*' | sed -e 's/^\.\///' -e '/^config\//d' \
 	-e '/^config$/d'
 ) | \
 (