Use dependencies for 'make headers_install'.

Re-export header files only if either they or their controlling Kbuild
file has actually changed. Also allow for similar dependencies with
'headers_check', once we properly create the dependencies for those.

Signed-off-by: David Woodhouse <dwmw2@infradead.org>

scripts/hdrcheck.sh

@@ -6,3 +6,5 @@ for FILE in `grep '^[ \t]*#[ \t]*include[ \t]*<' $2 | cut -f2 -d\< | cut -f1 -d\
 	exit 1
     fi
 done
+# FIXME: List dependencies into $3
+touch $3