cmd/llvmplugin: accept non-ABI pointer parameter attributes

[zhouguangyuan0718]

Summary

• retain supported noundef, nonnull, and align pointer parameter attributes during statepoint rewriting
• keep the existing ABI-affecting attribute checks fail closed
• add rewrite and codegen CTest coverage

Relationship

This is an independent prerequisite split from Go PR #32 after Go PR #33 merged. It does not change alloca root handling or write-barrier lowering.

Validation

• GoALLCStatepoints SupportedParamAttrsRewrite and SupportedParamAttrsCodegen: 2/2
• plugin rebuild against merged LLVM PR cmd/llvmplugin: propagate indirect statepoint calls #18
• git diff --check