mman: add MAP_EXCL flag for freebsd.

Author: devnexen

CHANGELOG.md

@@ -42,6 +42,8 @@ This project adheres to [Semantic Versioning](https://semver.org/).
   (#[1516](https://github.com/nix-rust/nix/pull/1516))
 - Added `Ipv4Ttl` and `Ipv6Ttl` sockopts.
   (#[1515](https://github.com/nix-rust/nix/pull/1515))
+- Added `MAP_EXCL` mmap flag for freebsd.
+  (#[1525](https://github.com/nix-rust/nix/pull/1525))
 
 ### Changed
 

src/sys/mman.rs

@@ -40,6 +40,10 @@ libc_bitflags!{
         MAP_PRIVATE;
         /// Place the mapping at exactly the address specified in `addr`.
         MAP_FIXED;
+        /// To be used with `MAP_FIXED`, to forbid the system
+        /// to select a different address than the one specified.
+        #[cfg(target_os = "freebsd")]
+        MAP_EXCL;
         /// Synonym for `MAP_ANONYMOUS`.
         MAP_ANON;
         /// The mapping is not backed by any file.