Mark posix_fallocate as supported on AIX (#1031)

AIX actually supports posix_fallocate procedure, although the fully
functioning fallocate is not available.

Author: ecnelises

src/backend/libc/fs/syscalls.rs

@@ -30,7 +30,6 @@ use crate::fs::AtFlags;
 #[cfg(not(any(
     netbsdlike,
     solarish,
-    target_os = "aix",
     target_os = "dragonfly",
     target_os = "espidf",
     target_os = "nto",
@@ -1616,7 +1615,6 @@ fn futimens_old(fd: BorrowedFd<'_>, times: &Timestamps) -> io::Result<()> {
     apple,
     netbsdlike,
     solarish,
-    target_os = "aix",
     target_os = "dragonfly",
     target_os = "espidf",
     target_os = "nto",

src/backend/libc/fs/types.rs

@@ -789,7 +789,6 @@ bitflags! {
 #[cfg(not(any(
     netbsdlike,
     solarish,
-    target_os = "aix",
     target_os = "espidf",
     target_os = "nto",
     target_os = "redox",

src/fs/fd.rs

@@ -10,7 +10,6 @@ use backend::fd::{AsFd, BorrowedFd};
 #[cfg(not(any(
     netbsdlike,
     solarish,
-    target_os = "aix",
     target_os = "dragonfly",
     target_os = "espidf",
     target_os = "nto",
@@ -231,7 +230,6 @@ pub fn futimens<Fd: AsFd>(fd: Fd, times: &Timestamps) -> io::Result<()> {
 #[cfg(not(any(
     netbsdlike,
     solarish,
-    target_os = "aix",
     target_os = "dragonfly",
     target_os = "espidf",
     target_os = "nto",