build-sys: prevent meson from downloading wrapped subprojects

The following patches are going to introduce meson wrap dependencies,
which is a solution to download and build missing dependencies.

The QEMU build-system will do network access with no way to avoid the
fallback. As a start, hardcode "--wrap-mode=nodownload" in configure, so
that wraps would be used only after a conscious decision of the user to
use "meson subprojects download" (before running configure).

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20230302131848.1527460-3-marcandre.lureau@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

configure

@@ -2615,6 +2615,10 @@ if test "$skip_meson" = no; then
 
   rm -rf meson-private meson-info meson-logs
 
+  # Prevent meson from automatically downloading wrapped subprojects when missing.
+  # You can use 'meson subprojects download' before running configure.
+  meson_option_add "--wrap-mode=nodownload"
+
   # Built-in options
   test "$bindir" != "bin" && meson_option_add "-Dbindir=$bindir"
   test "$default_feature" = no && meson_option_add -Dauto_features=disabled