This fixes a generic C99 compatibility issue in autoconf-generated
code.  No need to upstream this because the issue goes away if
autoconf is re-run.

diff --git a/configure b/configure
index 9d6084aa38e5d6e8..4d948816e1112d13 100755
--- a/configure
+++ b/configure
@@ -689,7 +689,7 @@ cat > conftest.$ac_ext << EOF
 #line 690 "configure"
 #include "confdefs.h"
 
-main(){return(0);}
+int main(){return(0);}
 EOF
 if { (eval echo configure:695: \"$ac_link\") 1>&5; (eval $ac_link) 2>&5; } && test -s conftest${ac_exeext}; then
   ac_cv_prog_cc_works=yes