Always set 'Vexec_path' before 'Vinvocation_directory' (bug#43137)

Always set 'Vexec_path' before 'Vinvocation_directory' (bug#43137)

Do this as depending on the OS if argv0 is not populated 'Vexec_path'
is used to infer 'Vinvocation_directory'.

     	* src/pdumper.c (pdumper_load): Invoke 'init_vars_for_load' instead
	of 'set_invocation_vars'.

	* src/lisp.h: Extern 'init_vars_for_load' instead of
	'set_invocation_vars' .

	* src/emacs.c (set_invocation_vars): Make it static and remove
	double invocation guard.
	(init_vars_for_load): Wrap 'init_callproc_1' and 'set_invocation_vars'
	calls + add double invocation guard.
	(init_cmdargs): Move out 'set_invocation_vars' invocation.
	(main): Call 'init_vars_for_load' instead of 'init_callproc_1'.