need remaining copts in previous commit

-D_GNU_SOURCE - Enables all GNU extensions
-D_POSIX_C_SOURCE=200809L - Enables POSIX.1-2008 features
-D_XOPEN_SOURCE=600 - Enables X/Open System Interface (XSI) features

These macros should make the necessary POSIX terminal functions (grantpt, posix_openpt, ptsname, unlockpt) available to CGo when building the Go standard library.
The error occurred because these functions are part of the POSIX terminal interface, and they need to be explicitly enabled through feature test macros when building with certain C library implementations.

Author: chrisirhc

toolchain/private/defs.bzl

@@ -162,7 +162,9 @@ def _target_linux_gnu(gocpu, zigcpu, glibc_version):
         dynamic_library_linkopts = [],
         supports_dynamic_linker = True,
         copts = [
+            "-D_GNU_SOURCE",
             "-D_POSIX_C_SOURCE=200809L",
+            "-D_XOPEN_SOURCE=600",
         ],
         libc = "glibc",
         bazel_target_cpu = "k8",