Don't misinterpret doc string as initial value

* lisp/loadhist.el (loadhist--restore-autoload):
* lisp/progmodes/vhdl-mode.el (vhdl-font-lock-keywords-0):
Prevent the doc string from being used as initial value.

lisp/loadhist.el

@@ -173,7 +173,7 @@ documentation of `unload-feature' for details.")
 ;; we undefine it.
 ;; So we use this auxiliary variable to keep track of the last (t . SYMBOL)
 ;; that occurred.
-(defvar loadhist--restore-autoload
+(defvar loadhist--restore-autoload nil
   "If non-nil, this is a symbol for which we should
 restore a previous autoload if possible.")
 

lisp/progmodes/vhdl-mode.el

@@ -13334,7 +13334,7 @@ File statistics: \"%s\"\n\
 (defvar vhdl-font-lock-keywords nil
   "Regular expressions to highlight in VHDL Mode.")
 
-(defvar vhdl-font-lock-keywords-0
+(defvar vhdl-font-lock-keywords-0 nil
   ;; set in `vhdl-font-lock-init' because dependent on user options
   "For consideration as a value of `vhdl-font-lock-keywords'.
 This does highlighting of template prompts and directives (pragmas).")