Try harder to detect unavailability of __builtin_mul_overflow(int64).

Commit c04d35f44 didn't quite do the job here, because it still allowed
the compiler to deduce that the function call could be optimized away.
Prevent that by putting the arguments and results in global variables.

Discussion: https://postgr.es/m/20171213213754.pydkyjs6bt2hvsdb@alap3.anarazel.de

1 files changed, 5 insertions, 4 deletions

diff --git a/configure b/configure
index 22ca4230fce..d9b7b8d7ec7 100755
--- a/configure
+++ b/configure
@@ -14485,14 +14485,15 @@ else
   cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
-int
-main ()
-{
 PG_INT64_TYPE a = 1;
 PG_INT64_TYPE b = 1;
 PG_INT64_TYPE result;
-__builtin_mul_overflow(*(volatile PG_INT64_TYPE *) a, *(volatile PG_INT64_TYPE *) b, &result);
+int oflo;
 
+int
+main ()
+{
+oflo = __builtin_mul_overflow(a, b, &result);
   ;
   return 0;
 }