adding KERNEL_VERSION macro for linux.

libc-test/semver/linux.txt

@@ -1146,6 +1146,7 @@ J1939_PGN_ADDRESS_COMMANDED
 J1939_PGN_MAX
 J1939_PGN_PDU1_MAX
 J1939_PGN_REQUEST
+KERNEL_VERSION
 KEYCTL_ASSUME_AUTHORITY
 KEYCTL_CHOWN
 KEYCTL_CLEAR

libc-test/test/linux_kernel_version.rs

@@ -0,0 +1,17 @@
+//! Compare libc's KERNEL_VERSION macro against a specific kernel version.
+
+extern crate libc;
+
+#[cfg(
+    target_os = "linux",
+)]
+mod t {
+    use libc;
+
+    #[test]
+    fn test_kernel_version() {
+        unsafe {
+            assert_eq!(libc::KERNEL_VERSION(6, 0, 0), 393216);
+        }
+    }
+}

src/unix/linux_like/mod.rs

@@ -1615,6 +1615,14 @@ safe_f! {
     pub {const} fn IPTOS_ECN(x: u8) -> u8 {
         x & ::IPTOS_ECN_MASK
     }
+
+    #[allow(ellipsis_inclusive_range_patterns)]
+    pub {const} fn KERNEL_VERSION(a: u32, b: u32, c: u32) -> u32 {
+        ((a << 16) + (b << 8)) + match c {
+            0 ... 255 => c,
+            _ => 255,
+        }
+    }
 }
 
 extern "C" {