Avoid usage of thread_local on DragonFlyBSD

__error() has been deprecated and return the same value as
__errno_location(). Removing the __error() function eliminates the sole
use of thread_local in this crate.

(backport <#3653>)
(cherry picked from commit de76fee)
[ resolved conflicts in all files and removed the now-unused
  `rustc_dep_of_std` - Trevor ]

Author: bjorn3

build.rs

@@ -18,7 +18,6 @@ const ALLOWED_CFGS: &[&str] = &[
     // Corresponds to `_TIME_BITS=64` in glibc
     "gnu_time_bits64",
     "libc_deny_warnings",
-    "libc_thread_local",
     // Corresponds to `__USE_TIME_BITS64` in UAPI
     "linux_time_bits64",
     "musl_v1_2_3",
@@ -47,7 +46,6 @@ fn main() {
     println!("cargo:rerun-if-changed=build.rs");
 
     let (rustc_minor_ver, _is_nightly) = rustc_minor_nightly();
-    let rustc_dep_of_std = env::var("CARGO_FEATURE_RUSTC_DEP_OF_STD").is_ok();
     let libc_ci = env::var("LIBC_CI").is_ok();
     let target_env = env::var("CARGO_CFG_TARGET_ENV").unwrap_or_default();
     let target_os = env::var("CARGO_CFG_TARGET_OS").unwrap_or_default();
@@ -143,11 +141,6 @@ fn main() {
         set_cfg("libc_deny_warnings");
     }
 
-    // #[thread_local] is currently unstable
-    if rustc_dep_of_std {
-        set_cfg("libc_thread_local");
-    }
-
     // Since Rust 1.80, configuration that isn't recognized by default needs to be provided to
     // avoid warnings.
     if rustc_minor_ver >= 80 {

libc-test/build.rs

@@ -72,10 +72,6 @@ fn do_ctest() {
 fn ctest_cfg() -> ctest::TestGenerator {
     let mut cfg = ctest::TestGenerator::new();
     cfg.skip_private(true);
-    let libc_cfgs = ["libc_thread_local"];
-    for f in &libc_cfgs {
-        cfg.cfg(f, None);
-    }
     cfg
 }
 

src/lib.rs

@@ -26,7 +26,6 @@
 #![cfg_attr(libc_deny_warnings, deny(warnings))]
 // Attributes needed when building as part of the standard library
 #![cfg_attr(feature = "rustc-dep-of-std", feature(link_cfg, no_core))]
-#![cfg_attr(libc_thread_local, feature(thread_local))]
 #![cfg_attr(feature = "rustc-dep-of-std", allow(internal_features))]
 // DIFF(1.0): The thread local references that raise this lint were removed in 1.0
 #![cfg_attr(feature = "rustc-dep-of-std", allow(static_mut_refs))]

src/unix/bsd/freebsdlike/dragonfly/errno.rs

@@ -1625,11 +1625,3 @@ extern "C" {
         entry: vm_map_entry_t,
     ) -> vm_map_entry_t;
 }
-
-// DIFF(main): module removed in de76fee6
-cfg_if! {
-    if #[cfg(libc_thread_local)] {
-        mod errno;
-        pub use self::errno::*;
-    }
-}