refactor: annotate RAND_MAX unstable in FreeBSD

This symbol has been modified in the last few versions of FreeBSD. It
can possibly be assumed that the constant is likely to change upstream,
and users should likely be advised of its use.

The link in the doc comment is broken until #5179 gets merged.

Author: dybucc

src/unix/bsd/freebsdlike/freebsd/freebsd11/mod.rs

@@ -259,7 +259,11 @@ s! {
 }
 
 pub const ELAST: c_int = 96;
-pub const RAND_MAX: c_int = 0x7fff_fffd;
+
+ct! {
+    pub const RAND_MAX: c_int = 0x7fff_fffd;
+}
+
 pub const KI_NSPARE_PTR: usize = 6;
 pub const MINCORE_SUPER: c_int = 0x20;
 /// max length of devicename

src/unix/bsd/freebsdlike/freebsd/freebsd12/mod.rs

@@ -303,7 +303,10 @@ s! {
     }
 }
 
-pub const RAND_MAX: c_int = 0x7fff_fffd;
+ct! {
+    pub const RAND_MAX: c_int = 0x7fff_fffd;
+}
+
 pub const ELAST: c_int = 97;
 
 /// max length of devicename

src/unix/bsd/freebsdlike/freebsd/freebsd13/mod.rs

@@ -316,7 +316,10 @@ s! {
     }
 }
 
-pub const RAND_MAX: c_int = 0x7fff_ffff;
+ct! {
+    pub const RAND_MAX: c_int = 0x7fff_ffff;
+}
+
 pub const ELAST: c_int = 97;
 
 pub const KF_TYPE_EVENTFD: c_int = 13;

src/unix/bsd/freebsdlike/freebsd/freebsd14/mod.rs

@@ -318,7 +318,10 @@ s! {
     }
 }
 
-pub const RAND_MAX: c_int = 0x7fff_ffff;
+ct! {
+    pub const RAND_MAX: c_int = 0x7fff_ffff;
+}
+
 pub const ELAST: c_int = 97;
 
 pub const KF_TYPE_EVENTFD: c_int = 13;

src/unix/bsd/freebsdlike/freebsd/freebsd15/mod.rs

@@ -320,7 +320,10 @@ s! {
     }
 }
 
-pub const RAND_MAX: c_int = 0x7fff_ffff;
+ct! {
+    pub const RAND_MAX: c_int = 0x7fff_ffff;
+}
+
 pub const ELAST: c_int = 97;
 
 pub const KF_TYPE_EVENTFD: c_int = 13;