unix: add preadv2 and pwritev2 to android and linux.

Add preadv2 and pwrite2 to linux and Android, to allow using the new flags
introduced in #4452.
Move definitions from musl and gnu to linux/mod.rs instead of each
separate system alone.
Skip test on Android due to the definitions being introduced in API 33

Author: Elie-Kh

libc-test/build.rs

@@ -2205,6 +2205,9 @@ fn test_android(target: &str) {
             // Added in API level 30, but tests use level 28.
             "memfd_create" | "mlock2" | "renameat2" | "statx" | "statx_timestamp" => true,
 
+            // Added in API level 33, but tests use level 28.
+            "preadv2" | "pwritev2" => true,
+
             // Added in glibc 2.25.
             "getentropy" => true,
 

src/unix/linux_like/android/mod.rs

@@ -3747,6 +3747,20 @@ extern "C" {
         newpath: *const c_char,
         flags: c_uint,
     ) -> c_int;
+    pub fn preadv2(
+        fd: c_int,
+        iov: *const crate::iovec,
+        iovcnt: c_int,
+        offset: off_t,
+        flags: c_int,
+    ) -> ssize_t;
+    pub fn pwritev2(
+        fd: c_int,
+        iov: *const crate::iovec,
+        iovcnt: c_int,
+        offset: off_t,
+        flags: c_int,
+    ) -> ssize_t;
 }
 
 cfg_if! {

src/unix/linux_like/linux/gnu/mod.rs

@@ -1029,22 +1029,6 @@ extern "C" {
         dirfd: c_int,
         path: *const c_char,
     ) -> c_int;
-    #[cfg_attr(gnu_file_offset_bits64, link_name = "preadv64v2")]
-    pub fn preadv2(
-        fd: c_int,
-        iov: *const crate::iovec,
-        iovcnt: c_int,
-        offset: off_t,
-        flags: c_int,
-    ) -> ssize_t;
-    #[cfg_attr(gnu_file_offset_bits64, link_name = "pwritev64v2")]
-    pub fn pwritev2(
-        fd: c_int,
-        iov: *const crate::iovec,
-        iovcnt: c_int,
-        offset: off_t,
-        flags: c_int,
-    ) -> ssize_t;
     pub fn preadv64v2(
         fd: c_int,
         iov: *const crate::iovec,

src/unix/linux_like/linux/mod.rs

@@ -4360,6 +4360,22 @@ extern "C" {
         flags: c_int,
     ) -> c_int;
     pub fn open_by_handle_at(mount_fd: c_int, handle: *mut file_handle, flags: c_int) -> c_int;
+    #[cfg_attr(gnu_file_offset_bits64, link_name = "preadv64v2")]
+    pub fn preadv2(
+        fd: c_int,
+        iov: *const crate::iovec,
+        iovcnt: c_int,
+        offset: off_t,
+        flags: c_int,
+    ) -> ssize_t;
+    #[cfg_attr(gnu_file_offset_bits64, link_name = "pwritev64v2")]
+    pub fn pwritev2(
+        fd: c_int,
+        iov: *const crate::iovec,
+        iovcnt: c_int,
+        offset: off_t,
+        flags: c_int,
+    ) -> ssize_t;
 }
 
 // LFS64 extensions

src/unix/linux_like/linux/musl/mod.rs

@@ -780,20 +780,6 @@ extern "C" {
         dirfd: c_int,
         path: *const c_char,
     ) -> c_int;
-    pub fn preadv2(
-        fd: c_int,
-        iov: *const crate::iovec,
-        iovcnt: c_int,
-        offset: off_t,
-        flags: c_int,
-    ) -> ssize_t;
-    pub fn pwritev2(
-        fd: c_int,
-        iov: *const crate::iovec,
-        iovcnt: c_int,
-        offset: off_t,
-        flags: c_int,
-    ) -> ssize_t;
     pub fn getauxval(type_: c_ulong) -> c_ulong;
     pub fn renameat2(
         olddirfd: c_int,