tests/feature_check/int_big: Rework "big int" detection.

MICROPY_LONGINT_IMPL_LONGLONG doesn't have overflow detection, so just
parsing a large number won't give an error, we need to print it out
to check that the whole number was parsed.

tests/feature_check/int_big.py

@@ -1,2 +1,2 @@
 # Check whether arbitrary-precision integers (MPZ) are supported
-1000000000000000000000000000000000000000000000
+print(1000000000000000000000000000000000000000000000)

tests/feature_check/int_big.py.exp

@@ -0,0 +1 @@
+1000000000000000000000000000000000000000000000

tests/run-tests

@@ -209,7 +209,7 @@ def run_tests(pyb, tests, args):
 
     # Check if arbitrary-precision integers are supported, and skip such tests if it's not
     native = run_micropython(pyb, args, 'feature_check/int_big.py')
-    if native == b'CRASH':
+    if native != b'1000000000000000000000000000000000000000000000\n':
         skip_int_big = True
 
     # Check if set type (and set literals) is supported, and skip such tests if it's not