Supports compilation with GOOS=aix (#1723)

Signed-off-by: Nuno Cruces <ncruces@users.noreply.github.com>

Makefile

@@ -218,6 +218,8 @@ check:
 	@GOARCH=wasm GOOS=js go build ./...
 # Ensure we build on gojs. See #1526.
 	@GOARCH=wasm GOOS=wasip1 go build ./...
+# Ensure we build on aix. See #1723
+	@GOARCH=ppc64 GOOS=aix go build ./...
 # Ensure we build on windows:
 	@GOARCH=amd64 GOOS=windows go build ./...
 # Ensure we build on an arbitrary operating system:

experimental/sys/syscall_errno.go

@@ -1,4 +1,4 @@
-//go:build !plan9
+//go:build !plan9 && !aix
 
 package sys
 

experimental/sys/syscall_errno_unsupported.go

@@ -1,3 +1,5 @@
+//go:build plan9 || aix
+
 package sys
 
 func syscallToErrno(err error) (Errno, bool) {