Shell: Add a 'setopt' builtin

This builtin sets (and unsets) boolean flags that alter the behaviour of
the shell.
The only flags added are
- inline_exec_keep_empty_segments: Keep empty segments in the result of
  splitting $(...) by $IFS
- verbose: Announce each command before executing it

It should be noted that the (rather extreme) verbosity of the names is
intentional, and will hopefully be alleviated by the next commit :^)

Shell/Shell.h

@@ -52,12 +52,17 @@
     __ENUMERATE_SHELL_BUILTIN(dirs)    \
     __ENUMERATE_SHELL_BUILTIN(pushd)   \
     __ENUMERATE_SHELL_BUILTIN(popd)    \
+    __ENUMERATE_SHELL_BUILTIN(setopt)  \
     __ENUMERATE_SHELL_BUILTIN(time)    \
     __ENUMERATE_SHELL_BUILTIN(jobs)    \
     __ENUMERATE_SHELL_BUILTIN(disown)  \
     __ENUMERATE_SHELL_BUILTIN(fg)      \
     __ENUMERATE_SHELL_BUILTIN(bg)
 
+#define ENUMERATE_SHELL_OPTIONS()                                                                                    \
+    __ENUMERATE_SHELL_OPTION(inline_exec_keep_empty_segments, false, "Keep empty segments in inline execute $(...)") \
+    __ENUMERATE_SHELL_OPTION(verbose, false, "Announce every command that is about to be executed")
+
 class Shell;
 
 class Shell : public Core::Object {
@@ -135,6 +140,15 @@ public:
         ReadLine,
     };
 
+#define __ENUMERATE_SHELL_OPTION(name, default_, description) \
+    bool name { default_ };
+
+    struct Options {
+        ENUMERATE_SHELL_OPTIONS();
+    } options;
+
+#undef __ENUMERATE_SHELL_OPTION
+
 private:
     Shell();
     virtual ~Shell() override;