Add MAP_SHARED_VALIDATE & MAP_SYNC

This pull adds two flags: MAP_SHARED_VALIDATE & MAP_SYNC implemented on
https://github.com/rust-lang/libc

The MAP_SHARED_VALIDATE flag was added to linux since 4.15, its a flag
that does two things: provide backwards compatibility with old mmap
implementations that don't check for flags, and allow new flags to be
added.

MAP_SYNC, on the other hand, was added to allow mmap to utilize Direct
Accses (DAX) on hardware that support it (non-volatile memory devices)
or in general: any ram-shaped filesystem.

both flags are available on both linux and android.

Author: sectordistrict

src/sys/mman.rs

@@ -41,6 +41,9 @@ libc_bitflags! {
         MAP_FILE;
         /// Share this mapping. Mutually exclusive with `MAP_PRIVATE`.
         MAP_SHARED;
+        /// Force mmap to check and fail on unknown flags. This also enables `MAP_SYNC`.
+        #[cfg(any(linux_android, target_os = "linux"))]
+        MAP_SHARED_VALIDATE;
         /// Create a private copy-on-write mapping. Mutually exclusive with `MAP_SHARED`.
         MAP_PRIVATE;
         /// Place the mapping at exactly the address specified in `addr`.
@@ -142,6 +145,9 @@ libc_bitflags! {
         /// Region grows down, like a stack.
         #[cfg(any(linux_android, freebsdlike, target_os = "openbsd"))]
         MAP_STACK;
+        /// Do not write through the page caches, write directly to the file. Used for Direct Access (DAX) enabled file systems. 
+        #[cfg(any(linux_android, target_os = "linux"))]
+        MAP_SYNC;
         /// Pages in this mapping are not retained in the kernel's memory cache.
         #[cfg(apple_targets)]
         MAP_NOCACHE;