Honor ./configure --cc= option

The cc variable is assigned before parsing command-line options.  This
effectively ignores the ./configure --cc= option.  Move the cc variable
assigned below option parsing.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/configure b/configure
index 4a8d352..7b1d79a 100755
--- a/configure
+++ b/configure
@@ -130,9 +130,6 @@
 targetos=""
 cpu=""
 
-cross_prefix=${cross_prefix-${CROSS_COMPILE}}
-cc="${CC-${cross_prefix}gcc}"
-
 # default options
 show_help="no"
 exit_val=0
@@ -175,6 +172,9 @@
   exit $exit_val
 fi
 
+cross_prefix=${cross_prefix-${CROSS_COMPILE}}
+cc="${CC-${cross_prefix}gcc}"
+
 if check_define __ANDROID__ ; then
   targetos="Android"
 elif check_define __linux__ ; then