tests/basics: Modify int-big tests to prevent constant folding.

So that these tests test the runtime behaviour, not the compiler (which may
be executed offline).

tests/basics/int_big_rshift.py

@@ -3,5 +3,7 @@ print(i >> 1)
 print(i >> 1000)
 
 # result needs rounding up
-print(-(1<<70) >> 80)
-print(-0xffffffffffffffff >> 32)
+i = -(1 << 70)
+print(i >> 80)
+i = -0xffffffffffffffff
+print(i >> 32)

tests/basics/int_big_xor.py

@@ -19,7 +19,8 @@ print((-a) ^ (1 << 100))
 print((-a) ^ (1 << 200))
 print((-a) ^ a == 0)
 print(bool((-a) ^ a))
-print(-1 ^ 0xffffffffffffffff) # carry overflows to higher digit
+i = -1
+print(i ^ 0xffffffffffffffff) # carry overflows to higher digit
 
 # test + -