Enable all debug flags when compiling in debug mode

[saghul]

They still need to be individually enabled either via API or with the -D CLI flag, but there is no need to modify the code and re-compile.

[bnoordhuis]

I think this broke something because I now get this when I start qjs:

$ ./build/qjs
js_link_module 'repl.js':
js_inner_module_linking done
js_inner_module_linking done
js_inner_module_linking done
js_inner_module_linking done
js_inner_module_evaluation 'repl.js':
js_inner_module_evaluation 'std':
js_inner_module_evaluation 'os':
js_inner_module_evaluation 'bjson':
QuickJS-ng - Type ".help" for help
qjs > 

[saghul]

Oh, I'll take a look!

[saghul]

@bnoordhuis Fix: #501