build: enable support for aix/ppc64

* Adds "aix/ppc64" to the cross-compile target list.
* Including AIX in the build tag of "metadata_other.go".
* Excluding AIX from the main ncdu build tags.
* Marking AIX as an unsupported platform for ncdu.
* Excluding AIX from the fallback redirect implementation.
* Excluding AIX from unix build tags to avoid undefined unix.WNOHANG.

lib/daemonize/daemon_other.go

@@ -1,4 +1,4 @@
-//go:build !unix
+//go:build !unix || aix
 
 // Package daemonize provides daemonization stub for non-Unix platforms.
 package daemonize

lib/daemonize/daemon_unix.go

@@ -1,4 +1,4 @@
-//go:build unix
+//go:build unix && !aix
 
 // Package daemonize provides daemonization interface for Unix platforms.
 package daemonize