vte: skip gobject-introspection with clang on arm

vte: skip gobject-introspection with clang on arm

For some as yet unknown reason, vte on arm (specifically, the qemuarm
and beaglebone-yocto machines at least) will fail during G-I code
generation (which runs the target binaries inside qemu-user):

    Bail out! VTE:ERROR:../sources/vte-0.80.3/src/vtegtk.cc:158:void
    style_provider_parsing_error_cb(GtkCssProvider *, void *, GError *):
    assertion failed (error == NULL): Expected an identifier (gtk-css-parser-error-quark, 1)

    qemu: uncaught target signal 6 (Aborted) - core dumped

Until this can be root-caused, we can disable G-I for this edge case.

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