Introduce and use compile_module_up

Introduce and use compile_module_up

This introduces compile_module_up, a unique pointer for
compile_module, and changes a few spots to use it.

gdb/ChangeLog
2020-09-23  Tom Tromey  <tom@tromey.com>

	* compile/compile.c (eval_compile_command): Update.
	* compile/compile-object-run.h (compile_object_run): Take a
	compile_module_up.
	* compile/compile-object-run.c (compile_object_run): Take a
	compile_module_up.
	* compile/compile-object-load.h (struct compile_module): Add
	constructor, destructor.
	(compile_module_up): New typedef.
	(compile_object_load): Return compile_object_up.
	* compile/compile-object-load.c (compile_object_load): Return
	compile_module_up.