Auto merge of #3376 - 0xcaff:martin/pthread_once, r=JohnTitor

Add pthread_once

Close #3157

Author: bors

libc-test/semver/linux.txt

@@ -1926,6 +1926,7 @@ PTHREAD_PRIO_PROTECT
 PTHREAD_PROCESS_PRIVATE
 PTHREAD_PROCESS_SHARED
 PTHREAD_STACK_MIN
+PTHREAD_ONCE_INIT
 PTRACE_ATTACH
 PTRACE_CONT
 PTRACE_DETACH
@@ -3373,6 +3374,8 @@ pthread_barrier_wait
 pthread_barrier_destroy
 pthread_barrierattr_t
 pthread_barrier_t
+pthread_once
+pthread_once_t
 ptrace
 ptsname_r
 pwrite64

src/unix/linux_like/linux/mod.rs

@@ -14,6 +14,7 @@ pub type nl_item = ::c_int;
 pub type idtype_t = ::c_uint;
 pub type loff_t = ::c_longlong;
 pub type pthread_key_t = ::c_uint;
+pub type pthread_once_t = ::c_int;
 pub type pthread_spinlock_t = ::c_int;
 
 pub type __u8 = ::c_uchar;
@@ -1903,6 +1904,7 @@ align_const! {
         size: [0; __SIZEOF_PTHREAD_RWLOCK_T],
     };
 }
+pub const PTHREAD_ONCE_INIT: pthread_once_t = 0;
 pub const PTHREAD_MUTEX_NORMAL: ::c_int = 0;
 pub const PTHREAD_MUTEX_RECURSIVE: ::c_int = 1;
 pub const PTHREAD_MUTEX_ERRORCHECK: ::c_int = 2;
@@ -4849,6 +4851,8 @@ extern "C" {
         longindex: *mut ::c_int,
     ) -> ::c_int;
 
+    pub fn pthread_once(control: *mut pthread_once_t, routine: extern "C" fn()) -> ::c_int;
+
     pub fn copy_file_range(
         fd_in: ::c_int,
         off_in: *mut ::off64_t,