Enable dylink tests under ubsan (emscripten-core#25606)

I don't remember why these were disabled but the whole `ubsan` suite
seems to still pass with this change.

I'm not why that missing realloc exports for withBuiltinMalloc were ok
in other configs but their absence from this list is clearly and
oversight.

Author: sbc100

test/common.py

@@ -1084,8 +1084,6 @@ def check_dylink(self):
       self.skipTest('dynamic linking not supported with llvm-libc')
     if self.is_wasm2js():
       self.skipTest('dynamic linking not supported with wasm2js')
-    if '-fsanitize=undefined' in self.cflags:
-      self.skipTest('dynamic linking not supported with UBSan')
     # MEMORY64=2 mode doesn't currently support dynamic linking because
     # The side modules are lowered to wasm32 when they are built, making
     # them unlinkable with wasm64 binaries.

tools/link.py

@@ -1568,10 +1568,12 @@ def limit_incoming_module_api():
     settings.REQUIRED_EXPORTS += [
       'malloc',
       'calloc',
+      'realloc',
       'memalign',
       'free',
       'emscripten_builtin_malloc',
       'emscripten_builtin_calloc',
+      'emscripten_builtin_realloc',
       'emscripten_builtin_memalign',
       'emscripten_builtin_free',
     ]