configure: Undefine _FORTIFY_SOURCE prior using it

Currently, we are enforcing the _FORTIFY_SOURCE=2 without any
previous detection if the macro has been already defined, e.g.
by environment, or is just enabled by compiler by default.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Signed-off-by: Jan Vesely <jano.vesely@gmail.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

diff --git a/configure b/configure
index 1b6f68b..8ad42bc 100755 (executable)
--- a/configure
+++ b/configure
@@ -3520,7 +3520,7 @@ if test "$gcov" = "yes" ; then
   CFLAGS="-fprofile-arcs -ftest-coverage -g $CFLAGS"
   LDFLAGS="-fprofile-arcs -ftest-coverage $LDFLAGS"
 elif test "$debug" = "no" ; then
-  CFLAGS="-O2 -D_FORTIFY_SOURCE=2 $CFLAGS"
+  CFLAGS="-O2 -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=2 $CFLAGS"
 fi