Remove extra check-cfg handled by libc directly

Author: Urgau

src/bootstrap/src/lib.rs

@@ -83,8 +83,6 @@ const EXTRA_CHECK_CFGS: &[(Option<Mode>, &str, Option<&[&'static str]>)] = &[
 (Some(Mode::Std),"no_global_oom_handling",None),
 (Some(Mode::Std),"no_rc",None),
 (Some(Mode::Std),"no_sync",None),
-(Some(Mode::Std),"freebsd12",None),
-(Some(Mode::Std),"freebsd13",None),
 (Some(Mode::Std),"backtrace_in_libstd",None),
 /* Extra values not defined in the built-in targets yet, but used in std */
 (Some(Mode::Std),"target_env",Some(&["libnx"])),