Fix a autoconf warning

configure.in

@@ -549,11 +549,11 @@ if test "$tor_cv_time_t_signed" != no; then
 fi
 
 AC_CACHE_CHECK([whether size_t is signed], tor_cv_size_t_signed, [
-AC_RUN_IFELSE(AC_LANG_SOURCE([
+AC_RUN_IFELSE([AC_LANG_SOURCE([
 #ifdef HAVE_SYS_TYPES_H
 #include <sys/types.h>
 #endif
-int main(int c, char**v) { if (((size_t)-1)<0) return 1; else return 0; }]),
+int main(int c, char**v) { if (((size_t)-1)<0) return 1; else return 0; }])],
   tor_cv_size_t_signed=no, tor_cv_size_t_signed=yes, tor_cv_size_t_signed=cross)
 ])