[Based on #2143 #2145 #2157] build: match cmd/link DWARF defaults

[cpunion]

Based on #2143, #2145, and #2157.

Problem

LLGo currently omits DWARF from linked binaries unless the caller explicitly passes -w=false. That is the opposite of cmd/link: linked Go binaries preserve DWARF by default, while -w removes it and -s implies -w unless an explicit -w=false overrides that implication.

Changing the default exercises the normal optimized DWARF path. The prerequisite PRs keep that pipeline valid, ignore storage-free Python frontend variables, and preserve precise runtime line sites on Darwin.

The default also exposed existing full-LTO verifier failures in functions with deferred calls. Defer execution blocks are emitted after the frontend instruction walk, so cleanup calls could be generated without !dbg. Range-over-func adds a second case: a defer can be registered in a synthetic yield function but emitted in its outer owner, where retaining the yield function lexical scope creates invalid cross-subprogram metadata.

Generating DWARF for the normal macOS package matrix also makes shard 0 exceed its previous 30-minute job budget. The first complete run reached later standard-library packages with no test failure before GitHub canceled the job at the hard timeout.

Changes

• preserve DWARF by default for linked executables, tests, installs, and C archives
• make -s imply -w, while preserving an explicit -s -w=false override
• match the cmd/link Darwin C-shared default: omit DWARF unless explicitly overridden
• keep ModeGen conservative because it has no final linker stage
• remove the temporary OmitDWARFByDefault policy field
• keep existing executable IR fixtures stable by making the cltest capture helper choose omission locally when the test did not request a DWARF mode
• resolve anonymous-function debug locations through their lexical function scope
• retain each defer statement source location while emitting its cleanup block
• for cross-function DeferTo, preserve line and column but reanchor the location to the outer owner DISubprogram
• cover ordinary and loop defer lowering at the SSA level, a real conditional-defer full-LTO link, and nested range-over-func defer metadata at O2
• keep the reduced test matrix unchanged, but allow its macOS shards 45 minutes; non-macOS shards remain capped at 30 minutes

The defer fixes stay inside defer lowering; they do not attach fallback locations to unrelated calls. The cltest helper does not change production defaults or mutate the caller configuration.

This PR does not implement native symbol-table stripping for -s, change pclntab mode selection, or add native LLDB Go-language support. The latter remains proposed in #2154.

Verification

• PR head adf396b6e: 40 checks passed, zero failed or pending; the conditional release job was skipped
• CI: Dev LTO GlobalDCE, Ubuntu/macOS platform coverage, all primary and compatibility shards, docs, targets, caches, and artifact tests passed
• CI: macOS shard 0 completed in 31m46s under the 45-minute platform-specific limit; shard 1 completed in 25m10s
• CI: Ubuntu, macOS, and full-LTO coverage uploads to Codecov completed successfully
• local diff-aware coverage for the [Based on #2143 #2145 #2157] build: match cmd/link DWARF defaults #2142 layer (bbe3f3a..adf396b6e): 45/45 coverable changed production-Go lines hit (100%)
• macOS: linker-option/default-policy tests, SSA debug-scope tests, and the previously completed full cl/cltest package
• macOS: full ./ssa suite with 91.9% package coverage; deferDebugLocation, deferDebugLocationFor, and setDeferDebugLocation each report 100%
• macOS: runtime Caller, CallersFrames, logging, panic, stack, statement-line, and explicit-DWARF line-site acceptance tests
• macOS: conditional-defer full-LTO regression, O2 nested range-over-func LLVM verification, and representative executable IR fixtures
• Ubuntu arm64 with Go 1.26.5 and LLVM 19: SSA defer-location tests, O2 nested range-over-func LLVM verification, conditional-defer full-LTO regression, explicit-DWARF line-site tests, and LTO plugin symbol matrices
• Ubuntu arm64: the original failing mkdirdemo passes with -lto=full -globaldce
• dependency CI: [Based on #2159] debug: keep optimization and SSA rewrites DWARF-safe #2143 and [Based on #2143] fix(pclntab): preserve Darwin line sites with DWARF #2157 each completed with 40 successful checks
• git diff --check upstream/main...HEAD

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

[gemini-code-assist]

Caution

The consumer version of Gemini Code Assist on GitHub has been sunset. All code review activity has officially ceased.

[codecov]

Codecov Report

❌ Patch coverage is 97.91667% 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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