pythongh-95853: Address wasm build and test issues

- pyexpat.c: readinst(): Use correct format char for int.
- Add workaround for Emscripten timezone issue with calculating tm_yday.
- Skip a decimal test that allocates a lot of memory. It sometimes fails
  on Emscripten.

Author: tiran

Lib/test/test_decimal.py

@@ -37,7 +37,7 @@
                           requires_legacy_unicode_capi, check_sanitizer)
 from test.support import (TestFailed,
                           run_with_locale, cpython_only,
-                          darwin_malloc_err_warning)
+                          darwin_malloc_err_warning, is_emscripten)
 from test.support.import_helper import import_fresh_module
 from test.support import threading_helper
 from test.support import warnings_helper
@@ -5605,6 +5605,7 @@ def __abs__(self):
     # Issue 41540:
     @unittest.skipIf(sys.platform.startswith("aix"),
                      "AIX: default ulimit: test is flaky because of extreme over-allocation")
+    @unittest.skipIf(is_emscripten, "Test is unstable on Emscripten")
     @unittest.skipIf(check_sanitizer(address=True, memory=True),
                      "ASAN/MSAN sanitizer defaults to crashing "
                      "instead of returning NULL for malloc failure.")

Modules/pyexpat.c

@@ -775,7 +775,7 @@ readinst(char *buf, int buf_size, PyObject *meth)
     Py_ssize_t len;
     const char *ptr;
 
-    str = PyObject_CallFunction(meth, "n", buf_size);
+    str = PyObject_CallFunction(meth, "i", buf_size);
     if (str == NULL)
         goto error;
 

Tools/wasm/wasm_build.py

@@ -191,7 +191,11 @@ def _check_emscripten():
     config_site=WASMTOOLS / "config.site-wasm32-emscripten",
     configure_wrapper=EMSCRIPTEN_ROOT / "emconfigure",
     make_wrapper=EMSCRIPTEN_ROOT / "emmake",
-    environ={"EM_COMPILER_WRAPPER": "ccache"} if HAS_CCACHE else {},
+    environ={
+        # workaround for https://github.com/emscripten-core/emscripten/issues/17635
+        "TZ": "UTC",
+        "EM_COMPILER_WRAPPER": "ccache" if HAS_CCACHE else None,
+    },
     check=_check_emscripten,
 )
 
@@ -352,12 +356,15 @@ def getenv(self) -> dict:
         env.setdefault("MAKEFLAGS", f"-j{os.cpu_count()}")
         platenv = self.host.platform.getenv(self)
         for key, value in platenv.items():
-            if isinstance(value, str):
-                value = value.format(
+            if value is None:
+                env.pop(key, None)
+            elif isinstance(value, str):
+                env[key] = value.format(
                     relbuilddir=self.builddir.relative_to(SRCDIR),
                     srcdir=SRCDIR,
                 )
-            env[key] = value
+            else:
+                env[key] = value
         return env
 
     def _run_cmd(self, cmd: Iterable[str], args: Iterable[str]):