[Based on #2143] fix(pclntab): preserve Darwin line sites with DWARF

[cpunion]

Based on #2143.

Problem

Darwin builds with DWARF currently disable every compiler-emitted funcinfo site record. That avoids an LLDB lexical-scope regression caused by inline assembly at function entry, but it also removes the final-PC anchors used to build precise runtime line tables. In larger binaries, runtime.Caller, runtime.CallersFrames, logging source prefixes, and panic locations can then fall back to an earlier address.

The two site classes have different debugger effects: function-entry and closure-stub address records alter the initial line-table row, while PC-line anchors are safe when the inline-assembly call itself has no debug location.

#2143 supplies the DWARF-safe optimized compilation pipeline. This PR is stacked on it so the explicit DWARF acceptance path is tested with the intended optimization behavior.

Changes

• add ssa.Builder.InlineAsmNoDebug, which clears only the emitted call location and preserves the builder current location
• emit PC-line anchors whenever funcinfo sites are enabled, including Darwin DWARF builds
• split runtime site policy into PC-line records and entry/stub address records
• suppress only entry/stub address records for embedded pclntab + Darwin + DWARF
• retain address records for Darwin without DWARF, external pclntab, and ELF targets
• add an explicit -ldflags=-w=false acceptance test for runtime.Caller, runtime.CallersFrames, and log.Lshortfile

This does not change pclntab mode selection, the default -w policy, runtime table format, or LLDB language behavior.

Fixes #2115.

Verification

• macOS: explicit-DWARF runtime line-site acceptance test
• macOS: current stacked head passed _lldb/runtest.sh, 198/198, plus the non-LLGo marker check
• Ubuntu arm64 with Go 1.26.5: SSA debug-location tests, site-policy tests, and runtime line-site acceptance test
• InlineAsmNoDebug, PC-line policy, address-site policy, and the funcinfo-site gate: 100% statement coverage in focused runs
• git diff --check upstream/main...HEAD

Ubuntu validation was limited to 2 CPUs, 15 GiB memory, and 512 PIDs.

[gemini-code-assist]

Caution

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[codecov]

Codecov Report

❌ Patch coverage is 95.65217% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
cl/static_init.go	87.50%	0 Missing and 1 partial ⚠️

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