`make compile_snippets` fails

[Matt Hainje]

Running make compile_snippets is broken.

1. There are several unknown tags in the Optimization chapter, e.g.:

Unhandled exception:
Invalid argument(s): Could not find tag 'adjust-alloc' in 'Optimization'.
#0      Book.findTag (package:tool/src/book.dart:186:5)
#1      main.<anonymous closure> (file:///Users/mattha/Projects/craftinginterpreters/tool/bin/compile_snippets.dart:308:42)
#2      MappedListIterable.elementAt (dart:_internal/iterable.dart:413:31)
#3      ListIterator.moveNext (dart:_internal/iterable.dart:342:26)
#4      main (file:///Users/mattha/Projects/craftinginterpreters/tool/bin/compile_snippets.dart:313:21)
#5      _delayEntrypointInvocation.<anonymous closure> (dart:isolate-patch/isolate_patch.dart:295:32)
#6      _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:192:12)
make: *** [compile_snippets] Error 255

2. The runtime-error-function snippet in the Closures chapter doesn't build:

FAIL Closures / runtime-error-function
      cc gen/snippets/chap25_closures/19-runtime-error-function/vm.c -std=c99 -Wall -Wextra -Werror -Wno-unused-parameter -Wno-unused-function -O3 -flto

gen/snippets/chap25_closures/19-runtime-error-function/vm.c:315:8: error: incompatible pointer types passing 'ObjFunction *' to parameter of type 'ObjClosure *' [-Werror,-Wincompatible-pointer-types]
  call(function, 0);
       ^~~~~~~~
gen/snippets/chap25_closures/19-runtime-error-function/vm.c:77:30: note: passing argument to parameter 'closure' here
static bool call(ObjClosure* closure, int argCount) {
                             ^
1 error generated.
make[1]: *** [build/release/chap25_closures-19-runtime-error-function/vm.o] Error 1

3. The look-for-existing-upvalues snippet in the Closurs chapter doesn't build:

FAIL Closures / look-for-existing-upvalue
      cc gen/snippets/chap25_closures/61-look-for-existing-upvalue/vm.c -std=c99 -Wall -Wextra -Werror -Wno-unused-parameter -Wno-unused-function -O3 -flto

gen/snippets/chap25_closures/61-look-for-existing-upvalue/vm.c:116:15: error: variable 'prevUpvalue' set but not used [-Werror,-Wunused-but-set-variable]
  ObjUpvalue* prevUpvalue = NULL;
              ^
1 error generated.
make[1]: *** [build/release/chap25_closures-61-look-for-existing-upvalue/vm.o] Error 1