Auto merge of #2888 - lwhsu:freebsd-CPU_SETSIZE, r=JohnTitor

Add CPU_SETSIZE const for FreeBSD

It's in all supported versions of FreeBSD.

Author: bors

libc-test/semver/freebsd.txt

@@ -173,6 +173,7 @@ CPU_LEVEL_CPUSET
 CPU_LEVEL_ROOT
 CPU_LEVEL_WHICH
 CPU_SET
+CPU_SETSIZE
 CPU_WHICH_CPUSET
 CPU_WHICH_IRQ
 CPU_WHICH_JAIL

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

@@ -1892,6 +1892,9 @@ pub const LIO_READV: ::c_int = 6;
 pub const DEVSTAT_N_TRANS_FLAGS: ::c_int = 4;
 pub const DEVSTAT_NAME_LEN: ::c_int = 16;
 
+// sys/cpuset.h
+pub const CPU_SETSIZE: ::c_int = 256;
+
 pub const SIGEV_THREAD_ID: ::c_int = 4;
 
 pub const EXTATTR_NAMESPACE_EMPTY: ::c_int = 0;