libc-test/build.rs: add netinet/in_pcb.h to the list of FreeBSD headers

(backport <#4482>)
(cherry picked from commit 8443057)

Author: kostikbel

libc-test/build.rs

@@ -2502,6 +2502,8 @@ fn test_freebsd(target: &str) {
                 "sys/sem.h",
                 "sys/shm.h",
                 "sys/socket.h",
+                "sys/socketvar.h",
+                "netinet/in_pcb.h",	// must be after sys/socketvar.h
                 "sys/stat.h",
                 "sys/statvfs.h",
                 "sys/sysctl.h",