Use short timezone names in _tzset_js

Without this change then timezone names will be the long form (Pacific
Standard Time) rather than the short form (PST), and since TZNAME_MAX
in musl is 6 (same in POSIX) the long names were getting truncated.

Fixes emscripten-core#21582

Author: sbc100

src/library.js

@@ -645,12 +645,13 @@ addToLibrary({
 
     {{{ makeSetValue('daylight', '0', 'Number(winterOffset != summerOffset)', 'i32') }}};
 
-    function extractZone(date) {
-      var match = date.toTimeString().match(/\(([A-Za-z ]+)\)$/);
-      return match ? match[1] : "GMT";
-    };
+    var extractZone = (date) => date.toLocaleTimeString(undefined, {timeZoneName:'short'}).split(' ')[2];
     var winterName = extractZone(winter);
     var summerName = extractZone(summer);
+#if ASSERTIONS
+    assert(lengthBytesUTF8(winterName) <= {{{ cDefs.TZNAME_MAX }}}, `timezone name truncated to fix in TZNAME_MAX (${winterName})`);
+    assert(lengthBytesUTF8(summerName) <= {{{ cDefs.TZNAME_MAX }}}, `timezone name truncated to fix in TZNAME_MAX (${summerName})`);
+#endif
     if (summerOffset < winterOffset) {
       // Northern hemisphere
       stringToUTF8(winterName, std_name, {{{ cDefs.TZNAME_MAX + 1 }}});

test/runner.py

@@ -135,7 +135,7 @@ def get_all_tests(modules):
 
 
 def get_crossplatform_tests(modules):
-  suites = ['core2', 'other'] # We don't need all versions of every test
+  suites = ['core0', 'other'] # We don't need all versions of every test
   crossplatform_tests = []
   # Walk over the test suites and find the test functions with the
   # is_crossplatform_test attribute applied by @crossplatform decorator

test/test_core.py

@@ -2656,6 +2656,7 @@ def test_strptime_reentrant(self):
     self.set_setting('EXIT_RUNTIME')
     self.do_core_test('test_strptime_reentrant.c')
 
+  @crossplatform
   def test_strftime(self):
     self.do_core_test('test_strftime.c')