libpcre: use libtool to install test binaries

libpcre: use libtool to install test binaries

If libtool builds a binary it's best to use libtool to install it, as
otherwise you might install a wrapper script or need to make assumptions
about where libtool has put the real binary (as this isn't always .libs)

Also use install instead of cp to install more files.

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Antonin Godard <antonin.godard@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>