fix: preserve local constant pools

[zhangzhenghao]

Summary

• parse compiler-emitted integer data directives, including .xword and .dword, with target byte order
• collect multi-line local constant-pool symbols without treating them as code labels
• preserve amd64 RIP-relative, arm64 ADRP/LO12, riscv64 PC-relative, loong64 PC-relative, s390x LARL, and ppc64le TOC relocations as Go symbol references
• run constant-pool value checks from the universal test suite on every supported architecture

Tests

• go test ./... -count=1
• go vet ./...
• generate and assemble tests/src/universal.c for amd64, arm64, riscv64, loong64, s390x, and ppc64le
• execute an amd64 standalone runtime probe for vector and floating-point constants
• GitHub Actions cross-platform/QEMU matrix

Closes #78