Merge branch 'ps/no-writable-strings'

Building with "-Werror -Wwrite-strings" is now supported.

* ps/no-writable-strings: (27 commits)
  config.mak.dev: enable `-Wwrite-strings` warning
  builtin/merge: always store allocated strings in `pull_twohead`
  builtin/rebase: always store allocated string in `options.strategy`
  builtin/rebase: do not assign default backend to non-constant field
  imap-send: fix leaking memory in `imap_server_conf`
  imap-send: drop global `imap_server_conf` variable
  mailmap: always store allocated strings in mailmap blob
  revision: always store allocated strings in output encoding
  remote-curl: avoid assigning string constant to non-const variable
  send-pack: always allocate receive status
  parse-options: cast long name for OPTION_ALIAS
  http: do not assign string constant to non-const field
  compat/win32: fix const-correctness with string constants
  pretty: add casts for decoration option pointers
  object-file: make `buf` parameter of `index_mem()` a constant
  object-file: mark cached object buffers as const
  ident: add casts for fallback name and GECOS
  entry: refactor how we remove items for delayed checkouts
  line-log: always allocate the output prefix
  line-log: stop assigning string constant to file parent buffer
  ...

wt-status.c

@@ -2409,7 +2409,7 @@ static void wt_porcelain_v2_print_unmerged_entry(
 		int mode;
 		struct object_id oid;
 	} stages[3];
-	char *key;
+	const char *key;
 	char submodule_token[5];
 	char unmerged_prefix = 'u';
 	char eol_char = s->null_termination ? '\0' : '\n';