closes bpo-31650: PEP 552 (Deterministic pycs) implementation (#4575)

Python now supports checking bytecode cache up-to-dateness with a hash of the
source contents rather than volatile source metadata. See the PEP for details.

While a fairly straightforward idea, quite a lot of code had to be modified due
to the pervasiveness of pyc implementation details in the codebase. Changes in
this commit include:

- The core changes to importlib to understand how to read, validate, and
  regenerate hash-based pycs.

- Support for generating hash-based pycs in py_compile and compileall.

- Modifications to our siphash implementation to support passing a custom
  key. We then expose it to importlib through _imp.

- Updates to all places in the interpreter, standard library, and tests that
  manually generate or parse pyc files to grok the new format.

- Support in the interpreter command line code for long options like
  --check-hash-based-pycs.

- Tests and documentation for all of the above.

Python/getopt.c

@@ -51,7 +51,8 @@ void _PyOS_ResetGetOpt(void)
     opt_ptr = L"";
 }
 
-int _PyOS_GetOpt(int argc, wchar_t **argv, wchar_t *optstring)
+int _PyOS_GetOpt(int argc, wchar_t **argv, wchar_t *optstring,
+                 const _PyOS_LongOption *longopts, int *longindex)
 {
     wchar_t *ptr;
     wchar_t option;
@@ -86,13 +87,41 @@ int _PyOS_GetOpt(int argc, wchar_t **argv, wchar_t *optstring)
             return 'V';
         }
 
-
         opt_ptr = &argv[_PyOS_optind++][1];
     }
 
     if ((option = *opt_ptr++) == L'\0')
         return -1;
 
+    if (option == L'-') {
+        // Parse long option.
+        if (*opt_ptr == L'\0') {
+            fprintf(stderr, "expected long option\n");
+            return -1;
+        }
+        *longindex = 0;
+        const _PyOS_LongOption *opt;
+        for (opt = &longopts[*longindex]; opt->name; opt = &longopts[++(*longindex)]) {
+            if (!wcscmp(opt->name, opt_ptr))
+                break;
+        }
+        if (!opt->name) {
+            fprintf(stderr, "unknown option %ls\n", argv[_PyOS_optind - 1]);
+            return '_';
+        }
+        opt_ptr = L"";
+        if (!opt->has_arg) {
+            return opt->val;
+        }
+        if (_PyOS_optind >= argc) {
+            fprintf(stderr, "Argument expected for the %ls options\n",
+                    argv[_PyOS_optind - 1]);
+            return '_';
+        }
+        _PyOS_optarg = argv[_PyOS_optind++];
+        return opt->val;
+    }
+
     if (option == 'J') {
         if (_PyOS_opterr)
             fprintf(stderr, "-J is reserved for Jython\n");