build: fix indeterminacy of icu_locales value

`icu_locales` is generated by joining values from `set` data structure.
However, `set` doesn't guarantee an order, so the result of
`icu_locales` is not determined. For example, the result value could be
'en,root' or 'root,en'. This fix makes it deterministic.

The main reason of this fix is to restore the reproducibility of the
build because the value of `icu_locales` is embedded into `node` binary.

configure.py

@@ -1662,7 +1662,7 @@ def icu_download(path):
     o['variables']['icu_small'] = b(True)
     locs = set(options.with_icu_locales.split(','))
     locs.add('root')  # must have root
-    o['variables']['icu_locales'] = ','.join(str(loc) for loc in locs)
+    o['variables']['icu_locales'] = ','.join(str(loc) for loc in sorted(locs))
     # We will check a bit later if we can use the canned deps/icu-small
     o['variables']['icu_default_data'] = options.with_icu_default_data_dir or ''
   elif with_intl == 'full-icu':