split out pthread types for threads header

src/header/bits_pthreadoi/cbindgen.toml

@@ -0,0 +1,18 @@
+# POSIX header spec: https://pubs.opengroup.org/onlinepubs/9799919799/basedefs/pthread.h.html
+#
+# This type is split out to avoid importing all of pthread.h into other headers.
+#
+# POSIX headers that require PTHREAD_ONCE_INIT:
+# - pthread.h (where it should be defined)
+# - threads.h (for ONCE_FLAG_INIT)
+include_guard = "_RELIBC_BITS_PTHREAD_ONCE_INIT_H"
+after_includes = """
+#include <bits/pthreadonce-t.h> // for pthread_once_t from sys/types.h
+
+#define PTHREAD_ONCE_INIT ((pthread_once_t){0})
+"""
+language = "C"
+no_includes = true
+cpp_compat = true
+[enum]
+prefix_with_name = true

src/header/bits_pthreadoi/mod.rs

@@ -0,0 +1,5 @@
+//! `PTHREAD_ONCE_INIT` for `pthread.h` implementation.
+//!
+//! See <https://pubs.opengroup.org/onlinepubs/9799919799/basedefs/pthread.h.html>.
+//!
+//! Implemented via C define in cbindgen.