organize some TODO comments

src-self-hosted/Module.zig

@@ -1048,6 +1048,8 @@ pub fn init(gpa: *Allocator, options: InitOptions) !Module {
 
     // We put everything into the cache hash except for the root source file, because we want to
     // find the same binary and incrementally update it even if the file contents changed.
+    // TODO Look into storing this information in memory rather than on disk and solving
+    // serialization/deserialization of *all* incremental compilation state in a more generic way.
     const cache_dir = if (options.root_pkg) |root_pkg| root_pkg.root_src_dir else std.fs.cwd();
     var cache = try std.cache_hash.CacheHash.init(gpa, cache_dir, "zig-cache");
     errdefer cache.release();

src-self-hosted/main.zig

@@ -960,13 +960,7 @@ pub fn buildOutputType(
         .yes_default_path => try std.fmt.allocPrint(arena, "{}.h", .{root_name}),
     };
 
-    // TODO Remove this, we'll have this error emitted lazily only if the features would end
-    // up actually getting used.
-    //if (!build_options.have_llvm) {
-    //    if ((use_llvm orelse false) or (use_lld orelse false) or (use_clang orelse false))
-    //        fatal("-fLLVM, -fLLD, and -fClang unavailable: compiler not built with LLVM extensions enabled", .{});
-    //}
-
+    // TODO look into implementing compiler_id at build time so we don't have to compute it at runtime.
     const compiler_id = try introspect.resolveCompilerId(gpa);
 
     var module = Module.init(gpa, .{