emacs: make subr-x available in all libraries

Like `cl-lib' and `pcase', which are already available in all
libraries, `subr-x' also provided many useful functions that
we would like to use.

Making `subr-x' available in every library from the get-go means
that we can use the functions it defines without having to double
check every single time, whether the feature is already available
in the current library.

emacs/notmuch-draft.el

@@ -27,6 +27,7 @@
 
 (require 'cl-lib)
 (require 'pcase)
+(require 'subr-x)
 
 (require 'notmuch-maildir-fcc)
 (require 'notmuch-tag)

emacs/notmuch-lib.el

@@ -23,6 +23,7 @@
 
 (require 'cl-lib)
 (require 'pcase)
+(require 'subr-x)
 
 (require 'mm-util)
 (require 'mm-view)

emacs/notmuch-message.el

@@ -23,6 +23,7 @@
 
 (require 'cl-lib)
 (require 'pcase)
+(require 'subr-x)
 
 (require 'message)
 (require 'notmuch-tag)

emacs/notmuch-parser.el

@@ -23,6 +23,7 @@
 
 (require 'cl-lib)
 (require 'pcase)
+(require 'subr-x)
 
 (defun notmuch-sexp-create-parser ()
   "Return a new streaming S-expression parser.