[cc] Fix sub-32-bit stack handling and incomplete struct resolution

[jgarzik]

Codegen fixes for char/short values on stack:

• x86_64: Use movzx for loading sub-32-bit values from stack/incoming args to avoid garbage in upper register bits. Store with AND mask to zero-extend.
• aarch64: Use correct sized load (ldrb/ldrh) which auto zero-extends, instead of forcing 32-bit loads that read adjacent garbage bytes.

IR linearization fix for incomplete struct types:

• Add resolve_struct_type() call in linearize_init_list_at_offset() to handle forward-declared struct typedefs in local variable initialization (the fix was already in convert_initializer for globals, but missing for locals).

Add regression tests:

• Unit test for incomplete struct type resolution via typedef
• Integration tests for char/short stack spill/reload scenarios

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR fixes two distinct codegen and IR linearization bugs related to sub-32-bit types and incomplete struct resolution:

• Codegen fixes: Corrects stack handling for char and short types to prevent garbage in upper register bits during load/reload operations
• IR linearization fix: Adds struct type resolution to handle forward-declared struct typedefs in local variable initialization
• Comprehensive tests: Adds regression tests covering both the codegen fixes and the incomplete struct resolution

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
cc/tests/datatypes/short.rs	Adds regression test short_stack_spill_reload to verify short values passed through stack preserve correct values without garbage bits
cc/tests/datatypes/char.rs	Adds regression test char_stack_spill_reload to verify char values passed through stack preserve correct values without garbage bits
cc/ir/test_linearize.rs	Adds unit test test_incomplete_struct_type_resolution to verify incomplete struct types are resolved to complete definitions during linearization
cc/ir/linearize.rs	Adds resolve_struct_type() calls in two locations to handle forward-declared struct typedefs in both ast_init_list_to_ir and linearize_init_list_at_offset
cc/arch/x86_64/codegen.rs	Implements movzx instruction for zero-extending sub-32-bit loads from stack/incoming args; implements zero-extend via AND mask for sub-32-bit stores
cc/arch/aarch64/codegen.rs	Uses appropriately sized load instructions (ldrb/ldrh) for sub-32-bit stack values, which auto zero-extend