Auto merge of #3457 - devnexen:fbsd_rfsigshare, r=JohnTitor

adding RFSIGSHARE flag for FreeBSD's rfork

Author: bors

libc-test/semver/freebsd.txt

@@ -1100,6 +1100,7 @@ RFLINUXTHPN
 RFMEM
 RFNOWAIT
 RFPROC
+RFSIGSHARE
 RFSPAWN
 RFTHREAD
 RFTSIGZMB

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

@@ -3891,6 +3891,7 @@ pub const RFMEM: ::c_int = 32;
 pub const RFNOWAIT: ::c_int = 64;
 pub const RFCFDG: ::c_int = 4096;
 pub const RFTHREAD: ::c_int = 8192;
+pub const RFSIGSHARE: ::c_int = 16384;
 pub const RFLINUXTHPN: ::c_int = 65536;
 pub const RFTSIGZMB: ::c_int = 524288;
 pub const RFSPAWN: ::c_int = 2147483648;