tree 2a9ee5c2392f6dfa8a723b36c876f10fe6f1bde9
parent aff544134bc9d29006f27adbe63d824dfe1436f6
author Fabian Meumertzheim <fabian@meumertzhe.im> 1787668358 -0700
committer Copybara-Service <copybara-worker@google.com> 1787668426 -0700

Add //cc/libc config settings for C standard libraries (#792)

Adds a new `//cc/libc` package with `config_setting`s for common C standard libraries, fed by a new `libc_flag` rule that exposes the current CC toolchain's `target_libc` value to `select()`. This mirrors the existing `//cc/compiler` package for compilers.

Covered libcs: `glibc`, `musl`, `uclibc`, `bionic`, `macosx` (Apple's libSystem, using the historical value set by toolchains for all Apple platforms), `freebsd`, `netbsd`, `openbsd`, `msvcrt`, `ucrt`, `msys`, `newlib`, `picolibc`, `llvm-libc`, and `wasi-libc`. Toolchains not shipped with Bazel are encouraged to use the same canonical names.

Since Bazel documents `target_libc` as "the libc version string (e.g. `glibc-2.2.2`)", `libc_flag` strips a version suffix (everything from the first `-` followed by a digit) before matching, so versioned values still match their family's setting while names like `wasi-libc` and `llvm-libc` are preserved.

The following changes make the new constraints usable:
* the auto-configured Unix toolchain detects the default libc via preprocessor macros and `-dumpmachine`
* the `target_libc` values emitted by the bundled Windows and BSD toolchain configs are changed to the correct values
* rule-based `cc_toolchain`s can declare their `target_libc` or fall back to a reasonable default

Closes #792

COPYBARA_INTEGRATE_REVIEW=https://github.com/bazelbuild/rules_cc/pull/792 from fmeum:libc-settings 7215a9ced75b2d01816d25b87e76c8387b0eee34
PiperOrigin-RevId: 970542238
Change-Id: Id569a70de73fc51ca8c69ca74169b8ba44cdc1bf