test:conv:hltohlbi: Add test for vararg builtins.

test/vast/Conversion/FromHL/ToHLBI/varargs.c

@@ -0,0 +1,18 @@
+// RUN: %vast-front -vast-emit-mlir=hl %s -o - | %vast-opt --vast-hl-to-hl-builtin | %file-check %s
+
+#include <stdarg.h>
+
+double average(int count, ...)
+{
+    va_list ap;
+    int j;
+    double tot = 0;
+    // CHECK: hlbi.va_start
+    va_start(ap, count); //Requires the last fixed parameter (to get the address)
+    for(j=0; j<count; j++)
+    // CHECK: hl.va_arg_expr
+        tot+=va_arg(ap, double); //Requires the type to cast to. Increments ap to the next argument.
+    // CHECK: hlbi.va_end
+    va_end(ap);
+    return tot/count;
+}