[llvm-branch-commits] [NFC][asan] Re-use ErrorGeneric::shadow_val (PR #195684)

[Vitaly Buka via llvm-branch-commits]

https://github.com/vitalybuka created https://github.com/llvm/llvm-project/pull/195684

This requires change in ErrorGeneric constructor, to now we skip partial
shadow only if next one has a better value.

Before shadow_val was either `0x[a-f].` or 0.
Now it may be partial granule as well.

However it's NFC as  `0 < shadow_val < ASAN_SHADOW_GRANULARITY` does not
affect reporting outside of `CheckPoisonRecords`.