libxl: provide xenlight.pc

libxl: provide xenlight.pc

A pkg-config file for libxl. It also contains two variables
(xenfirmwaredir and libexec_bin) so that tools that are very keen on
knowing the locations of Xen binaries (say, libvirt) can use them to
determine the location of the binaries.

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Cc: Ian Campbell <ian.campbell@citrix.com>
Cc: Ian Jackson <ian.jackson@eu.citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
[ ijc -- ran autogen.sh ]