unix: use errnoErr in generated wrappers on solaris

To prevent allocations at runtime for common errno values (EAGAIN,
EINVAL, ENOENT).

This was omitted from CL 8190 because the solaris port was broken
otherwise at that time.

Change-Id: I6061d071dddf34d0fd022e0ecfb854b01c56b723
Reviewed-on: https://go-review.googlesource.com/c/sys/+/528375
Reviewed-by: Heschi Kreinick <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Auto-Submit: Tobias Klauser <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Run-TryBot: Ian Lance Taylor <[email protected]>

Author: tklauser

unix/mksyscall_solaris.go

@@ -298,7 +298,7 @@ func main() {
 
 			if doErrno {
 				text += "\tif e1 != 0 {\n"
-				text += "\t\terr = e1\n"
+				text += "\t\terr = errnoErr(e1)\n"
 				text += "\t}\n"
 			}
 			text += "\treturn\n"