Auto merge of #2402 - devnexen:fbsd_map_prefault_read, r=JohnTitor

freebsd/dragonfly adding MAP_PREFAULT_READ/MAP_VPAGETABLE mmap flags.

Author: bors

libc-test/semver/freebsd.txt

@@ -676,6 +676,7 @@ MAP_FILE
 MAP_HASSEMAPHORE
 MAP_NOCORE
 MAP_NOSYNC
+MAP_PREFAULT_READ
 MAP_STACK
 MAXFREQ
 MAXPHASE

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

@@ -624,6 +624,7 @@ pub const Q_SETQUOTA: ::c_int = 0x800;
 
 pub const MAP_GUARD: ::c_int = 0x00002000;
 pub const MAP_EXCL: ::c_int = 0x00004000;
+pub const MAP_PREFAULT_READ: ::c_int = 0x00040000;
 pub const MAP_ALIGNED_SUPER: ::c_int = 1 << 24;
 
 pub const POSIX_FADV_NORMAL: ::c_int = 0;