The cc-option macro runs $(CC) in -S mode (generate assembly) to avoid a
pointless run of the assembler.  However, this does not work when you want
to detect support for cc->as option passthrough.  clang ignores -Wa unless
-c is provided, and exits successfully even if the -Wa,-32 option is not
supported.

Reported-by: Stefan Hajnoczi <stefanha@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-id: 1469043409-14033-1-git-send-email-pbonzini@redhat.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>