readline: install a .pc file

Some packages (such as udftools) fail to build against readline in
static linking configurations. To fix this, we install the .pc file
provided by readline.

Unfortunately, this .pc file is by default not correct, so a patch is
added to fix it, and this patch requires to re-autoconf the package
(but not autoreconf since only autoconf is used).

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>