Auto merge of #2822 - GuillaumeGomez:__error-alias, r=JohnTitor

Add doc aliases on __error() function

We recommend using `__errno_location` everywhere except on apple and freebsd targets, which is a bit confusing.

I can instead reexport it as `__errno_location` if you prefer?

Author: bors

src/unix/bsd/apple/mod.rs

@@ -5020,6 +5020,8 @@ extern "C" {
         thread_info_out: thread_info_t,
         thread_info_outCnt: *mut mach_msg_type_number_t,
     ) -> kern_return_t;
+    #[cfg_attr(doc, doc(alias = "__errno_location"))]
+    #[cfg_attr(doc, doc(alias = "errno"))]
     pub fn __error() -> *mut ::c_int;
     pub fn backtrace(buf: *mut *mut ::c_void, sz: ::c_int) -> ::c_int;
     pub fn backtrace_symbols(addrs: *const *mut ::c_void, sz: ::c_int) -> *mut *mut ::c_char;

src/unix/bsd/freebsdlike/freebsd/mod.rs

@@ -3835,6 +3835,8 @@ cfg_if! {
 }
 
 extern "C" {
+    #[cfg_attr(doc, doc(alias = "__errno_location"))]
+    #[cfg_attr(doc, doc(alias = "errno"))]
     pub fn __error() -> *mut ::c_int;
 
     pub fn aio_cancel(fd: ::c_int, aiocbp: *mut aiocb) -> ::c_int;