std.c: define MSG constants for solaris/illumos

Author: rzezeski

lib/std/c.zig

@@ -5776,6 +5776,20 @@ pub const MSG = switch (native_os) {
         pub const FBLOCKING = 0x10000;
         pub const FNONBLOCKING = 0x20000;
     },
+    .solaris, .illumos => struct {
+        pub const OOB = 0x0001;
+        pub const PEEK = 0x0002;
+        pub const DONTROUTE = 0x0004;
+        pub const EOR = 0x0008;
+        pub const CTRUNC = 0x0010;
+        pub const TRUNC = 0x0020;
+        pub const WAITALL = 0x0040;
+        pub const DONTWAIT = 0x0080;
+        pub const NOTIFICATION = 0x0100;
+        pub const NOSIGNAL = 0x0200;
+        pub const CMSG_CLOEXEC = 0x1000;
+        pub const CMSG_CLOFORK = 0x2000;
+    },
     else => void,
 };
 pub const SOCK = switch (native_os) {