Debug Builds
対象実装: このドキュメントは現行 Bootstrap 実装（
nepl-core/nepl-cli）の debug build 挙動を記述する。
NEPLg2.1 の正の仕様はdoc/2.1spec/を参照。
This document describes debug-only output and profile gates.
Profile gates
Use #if[profile=debug] or #if[profile=release] to include code only for a
given compiler profile.
The active profile is controlled by the CLI option:
--profile debug--profile release
If omitted, the compiler uses the build profile it was compiled with.
Debug output helpers
The stdlib provides debug output helpers that only emit in debug builds:
std/stdio::debugstd/stdio::debuglnstd/diag::diag_debug_printstd/diag::diag_debug_println
In release builds these functions are no-ops.