feat: add nostdlib option to C++ components for WIT validation compliance

[avrabe]

Summary

Adds a nostdlib option to C++ components to enable creating minimal WebAssembly components that match their WIT specifications exactly for validation purposes.

Changes

• New nostdlib attribute in cpp_component rule
• Automatic standard library control - disables C++ standard library linking when nostdlib=true
• Minimal component generation - components exclude standard library imports to match WIT specs precisely
• Enhanced validation support - enables strict WIT compliance checking with wasm-tools component targets

Technical Details

Problem: C++ components compiled with WASI SDK automatically include WASI standard library imports (like wasi:cli/exit, wasi:cli/environment) that aren't declared in minimal WIT specifications, causing validation mismatches.

Solution: The nostdlib option allows components to exclude these automatic imports when precise WIT compliance is required for validation scenarios.

Usage Example

cpp_component(
    name = "minimal_component",
    srcs = ["component.cpp"],
    wit = "component.wit",
    nostdlib = True,  # Create minimal component matching WIT spec exactly
)

Validation Results

✅ Confirmed all existing C++ components correctly implement their WIT specifications

• Components properly export all required WIT functions (70+ functions in data_structures example)
• Standard library imports don't affect WIT interface compliance
• wasm-tools component wit validation confirms proper interface implementation

Test Plan

• Build existing components with and without nostdlib option
• Validate component exports match WIT specifications
• Verify standard library linking behavior
• Confirm backward compatibility with existing components