If sys/soundcard.h is available, it is currently not possible to
disable OSS with the --disable-oss or --without-default-features
configure switches. Improve the check in meson.build to fix this.

Fixes: 87430d5b ("configure, meson: move audio driver detection to Meson")
Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20211102105822.773131-1-thuth@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>