M68K: Handle minimum signed displacements

[carrerasdarren-cell]

Your checklist for this pull request

• I've documented or updated the documentation of every API function and struct this PR changes.
• I've added tests that prove my fix is effective or that my feature works (if possible)

Detailed description

M68K displacement printing currently calls abs() on signed 32-bit values. abs(INT32_MIN) cannot be represented by int, so the operation has undefined behavior and triggers the public OSS-Fuzz report 484248078.

Convert negative displacements through a signed 64-bit intermediate before narrowing their magnitude to uint32_t. Apply the helper to base, inner, and outer 32-bit displacement formatting. Add regression coverage for both base-displacement and memory-indirect encodings at INT32_MIN.

Test plan

• xcrun clang-format --dry-run --Werror arch/M68K/M68KInstPrinter.c
• ASan/UBSan build with the original nine-byte OSS-Fuzz testcase
• ASan/UBSan disassembly of both new INT32_MIN cases
• cstest tests/details/m68k.yaml (444 tests passed)
• git diff --check

Closing issues

Closes #3040

[carrerasdarren-cell]

Closing this after finding #2990, which covers the same three M68K INT32_MIN displacement sites and already follows the requested SStream-helper design. I missed that prior work in the pre-publication search; apologies for the duplicate and reviewer noise.