Negative Binary Literals are Positive

[almann]

When implementing amazon-ion/ion-rust#214, I noticed in this commit that equiv testing was failing for binary notation of integers.

Specifically these two skip-list files:

    // ion-c seems to have a problem with negative binary literals amzn/ion-c#235
    "ion-tests/iontestdata/good/equivs/binaryInts.ion",
    "ion-tests/iontestdata/good/equivs/intsWithUnderscores.ion",

When running our Element tests in ion-rs, the values parse out as positive for the binary literals. I will add a direct reproduction in ion-c when I get a chance, but I wanted to make sure I cut the issue so we don't lose track of it.

[almann]

Verified in a unit test in IonC:

// reproduction for amzn/ion-c#235
TEST(IonTextInt, BinaryLiterals) {
    const char *ion_text = "-0b100";
    hREADER  reader;
    ION_TYPE type;
    int64_t value;

    ION_ASSERT_OK(ion_test_new_text_reader(ion_text, &reader));
    ION_ASSERT_OK(ion_reader_next(reader, &type));
    ASSERT_EQ(tid_INT, type);
    ION_ASSERT_OK(ion_reader_read_int64(reader, &value));
    ASSERT_EQ(-4, value);
}

Produces the following failure:

Failure
      Expected: -4
To be equal to: value
      Which is: 4