configure: Remove useless uses of ARCH_CFLAGS

configure: Remove useless uses of ARCH_CFLAGS

Remove some useless uses of ARCH_CFLAGS -- this variable was never set
so will always be empty. The uses were accidental: in commit 0c439cbf8
Juan Quintela removed ARCH_CFLAGS in favour of CFLAGS (which in turn
became QEMU_CFLAGS). However in commit be17dc90 a use of it was
reintroduced (apparently accidentally) by Michael S. Tsirkin, and then
I subsequently cut-n-pasted that into a number of other configure
feature tests.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Andreas Färber <afaerber@suse.de>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>