tools/libxc: Fix use of zlib-options when building the domain builder

tools/libxc: Fix use of zlib-options when building the domain builder

c/s de0f8c7c changed the use of zlib-options, and moved it from being locally
generated to coming from ./configure.

However, it neglected to modify the users of zlib-options.  The curious use of
$(call ...) was to select either the -D or -l options as appropriate, but c/s
de0f8c7c broke this by loosing the `grep`.

Instead, use $(filter ...) to pick out either the -D or -l options.  This
fixes the build with Clang, which complains at passing '-llzma' when trying
to compile xc_dom_bzimageloader.c to xc_dom_bzimageloader.o.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
Acked-by: Roger Pau Monné <roger.pau@citrix.com>