gawk: refactor

- Don't build with libsigsegv by default.  The build apparently attempted
  to link against it, but it never retained the reference anyway...
- Side effect: stdenv bootstrapping needs no libsigsegv anymore.
- Run checks, but only in the interactive gawk by default on Linux,
  so that stdenv bootstrap isn't slowed down (by glibc locales, etc.).
- xz should be no longer needed in inputs, as we have it in stdenvs now.

The whole change was triggered by some used kernel versions still
breaking libsigsegv tests #28464.

pkgs/stdenv/linux/default.nix

@@ -303,7 +303,10 @@ in
             gnumake gnused gnutar gnugrep gnupatch patchelf ed paxctl
           ]
         # Library dependencies
-        ++ map getLib [ attr acl zlib pcre libsigsegv ]
+        ++ map getLib (
+            [ attr acl zlib pcre ]
+            ++ lib.optional (gawk.libsigsegv != null) gawk.libsigsegv
+          )
         # More complicated cases
         ++ [
             glibc.out glibc.dev glibc.bin/*propagated from .dev*/ linuxHeaders