bash: use default PATH in FHS environments

If bash is executed within an environment where PATH is not set, it uses
the DEFAULT_PATH_VALUE compiled into bash to set PATH. In nixpkgs we set
this to /no-such-path by default. This makes sense in a nixpkgs/NixOS
environment since paths like /bin or /usr/bin should not be used.
However, when bash is used inside an FHS environment, this produces
results that differ from distributions which follow the FHS standard.

Before this change:
$ steam-run env -i /bin/bash -c 'echo $PATH'
/no-such-path

After this change:
$ steam-run env -i /bin/bash -c 'echo $PATH'
/usr/local/bin:/usr/local/sbin:/usr/bin:/usr/sbin:/bin:/sbin:.

pkgs/build-support/build-fhs-userenv-bubblewrap/env.nix

···
   basePkgs = with pkgs;
     [ glibcLocales
       (if isMultiBuild then glibc_multi else glibc)
-      (toString gcc.cc.lib) bashInteractive coreutils less shadow su
+      (toString gcc.cc.lib) bashInteractiveFHS coreutils less shadow su
       gawk diffutils findutils gnused gnugrep
       gnutar gzip bzip2 xz
     ];

pkgs/build-support/build-fhs-userenv/env.nix

···
   basePkgs = with pkgs;
     [ glibcLocales
       (if isMultiBuild then glibc_multi else glibc)
-      (toString gcc.cc.lib) bashInteractive coreutils less shadow su
+      (toString gcc.cc.lib) bashInteractiveFHS coreutils less shadow su
       gawk diffutils findutils gnused gnugrep
       gnutar gzip bzip2 xz
     ];

pkgs/shells/bash/5.1.nix

···
 , readline81 ? null
 , withDocs ? false
 , texinfo ? null
+, forFHSEnv ? false
 }:
 
 with lib;
···
   NIX_CFLAGS_COMPILE = ''
     -DSYS_BASHRC="/etc/bashrc"
     -DSYS_BASH_LOGOUT="/etc/bash_logout"
+  '' + optionalString (!forFHSEnv) ''
     -DDEFAULT_PATH_VALUE="/no-such-path"
     -DSTANDARD_UTILS_PATH="/no-such-path"
+  '' + ''
     -DNON_INTERACTIVE_LOGIN_SHELLS
     -DSSH_SOURCE_BASHRC
   '';

pkgs/top-level/all-packages.nix

···
     interactive = true;
     withDocs = true;
   };
+  bashInteractiveFHS = callPackage ../shells/bash/5.1.nix {
+    binutils = stdenv.cc.bintools;
+    interactive = true;
+    withDocs = true;
+    forFHSEnv = true;
+  };
 
   bash-completion = callPackage ../shells/bash/bash-completion { };