cmd/compile: add first-phase defer lowering for LLVM

[zhouguangyuan0718]

Implement first-phase classic defer support in the LLVM backend.

Summary:

• lower SSA BlockDefer to llvm.go.defer.edge callbr recovery CFG;
• preserve distinct deferproc, deferprocStack, and deferprocat pointer ABI shapes;
• keep open-coded defers on the classic path for now;
• propagate GoObj FuncID/FuncFlag so defer wrappers remain transparent to recover;
• add codegen, runtime, plugin GoObj, and defer regression coverage;
• qualify 113 newly passing runtime tests while keeping unrelated unstable GC cases out of this PR whitelist.

Whitelist on Darwin/arm64:

• codegen: 71 files
• runtime: 1068 files

The inherited llvm_alloca_statepoint_gc.go and llvm_newproc_gc.go cases are intentionally excluded here. The former is requalified by the scoped stack-object-root fix in #75; the latter remains a known runtime failure.

Dependencies:

• LLVM PR cmd/compile: expand LLVM nil checks after IR construction #38
• go-llvm PR cmd/compile: model nil closure loads without volatile #7

Validated with upstream defer/recover/range tests and focused LLVM/GoObj checks.

[zhouguangyuan0718]

LLVM blacklist probe (darwin/arm64)

Using the matching LLVM payload and GOALLC_FILECHECK, with a 40-minute suite timeout:

• codegen: 55 blacklist candidates; 47 pass compile+verifier, 6 skipped by platform/experiment build tags, 2 fail (mathbits.go / unsupported Ctz64; writebarrier.go / wbMove pointer-shape check).
• runtime: 166 candidates; 114 pass, 13 skipped by build tags, 38 fail; fixedbugs/issue29312.go was separately stopped after 10 minutes of continuous llc CPU and is recorded as one performance timeout.
• effective pass total: 161 cases; skipped: 19; failed/timeout: 41.

I did not bulk-promote these cases into test/llvm_tests.json: codegen passes without FileCheck are compile/verifier-only, and runtime failures include independent GoObj pointer-map, pcsp, traceback/debug-line, and test-harness issues that need separate qualification.

[zhouguangyuan0718]

Whitelist refresh is now scoped to this PR: 71 Darwin/arm64 codegen files and 1068 runtime files. The defer probe added 113 stable runtime cases. I removed llvm_alloca_statepoint_gc.go and llvm_newproc_gc.go from this layer because neither failure is fixed by defer lowering itself; #75 requalifies the alloca case after its scoped-root fix.