libuv: Include BSD sys/cpuset.h only on platforms where we use it

Since commit 43d6e5a71f (libuv: misc: add function to get CPU affinity
mask size, 2017-09-06, v3.12.0-rc1~412^2~3) we include `<sys/cpuset.h>`
on several BSD platforms but only use it on FreeBSD.

Utilities/cmlibuv/src/unix/core.c

@@ -72,8 +72,6 @@ extern char** environ;
 # include <sys/sysctl.h>
 # include <sys/filio.h>
 # include <sys/wait.h>
-# include <sys/param.h>
-# include <sys/cpuset.h>
 # if defined(__FreeBSD__)
 #  define uv__accept4 accept4
 # endif
@@ -82,6 +80,11 @@ extern char** environ;
 # endif
 #endif
 
+#if defined(__FreeBSD__)
+# include <sys/param.h>
+# include <sys/cpuset.h>
+#endif
+
 #if defined(__MVS__)
 #include <sys/ioctl.h>
 #endif