cmd/compile: encode LLVM ABI0 in function names

[zhouguangyuan0718]

Use the reserved <ABI0> suffix as the only LLVM storage-name
identity for ABI0 Go functions. ABIInternal function names remain
unchanged.

Remove goobj.symbol.name metadata emission from function, data, and
debug-info paths. Keep the LLVM calling convention as the lowering
contract while allowing GoObj to derive symbol ABI solely from the
function name.

Reject logical Go symbol names that already use the reserved suffix,
and update the cgo unsafe-argument codegen checks.

Update the pinned GoALLC LLVM payload to
goallc-llvm23.1.0-20260813T171727Z at
1d142acb4dab7262347b57ac341235913b210f40. Refresh the affected
plugin fixtures and ABI tests for native-Go small-leaf stack-check
elision and the PCDATA_StackMapIndex=-1 entry sentinel. No runtime
frontend support is included here.

Tested locally against the final LLVM source and plugin:

ctest --test-dir "$PLUGIN_BUILD" --output-on-failure -j 4
# 90/90 passed

GOALLC_LLVM_DIR="$PAYLOAD" ./bin/go test cmd/internal/testdir \
  -run '^TestLLVM/(abi-differential|alloca-statepoint|caller-state|getg-abi0-fail-closed|writebarrier-helpers|compile-only-regressions|writebarrier-ir)' \
  -count=1

./bin/go test -tags=llvm23,dynamicllvm cmd/compile/internal/ssa
./bin/go test cmd/llvmtoolexec