patch 8.0.0219: ubsan reports errors for overflow

Problem:    Ubsan reports errors for integer overflow.
Solution:   Define macros for minimum and maximum values.  Select an
            expression based on the value. (Mike Williams)
diff --git a/src/evalfunc.c b/src/evalfunc.c
index da22354..9ebd2df 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -3304,21 +3304,12 @@
 
     if (get_float_arg(argvars, &f) == OK)
     {
-# ifdef FEAT_NUM64
-	if (f < -0x7fffffffffffffffLL)
-	    rettv->vval.v_number = -0x7fffffffffffffffLL;
-	else if (f > 0x7fffffffffffffffLL)
-	    rettv->vval.v_number = 0x7fffffffffffffffLL;
+	if (f < -VARNUM_MAX)
+	    rettv->vval.v_number = -VARNUM_MAX;
+	else if (f > VARNUM_MAX)
+	    rettv->vval.v_number = VARNUM_MAX;
 	else
 	    rettv->vval.v_number = (varnumber_T)f;
-# else
-	if (f < -0x7fffffff)
-	    rettv->vval.v_number = -0x7fffffff;
-	else if (f > 0x7fffffff)
-	    rettv->vval.v_number = 0x7fffffff;
-	else
-	    rettv->vval.v_number = (varnumber_T)f;
-# endif
     }
 }