Merge pull request #73964 from kateinoigakukun/katei/enable-observation-wasm

[wasm] Enable Observation module build for Wasm target

Author: kateinoigakukun

utils/swift_build_support/swift_build_support/products/wasmstdlib.py

@@ -110,6 +110,7 @@ def _build(self, host_target, target_triple):
                                                'swift-experimental-string-processing'))
         self.cmake_options.define('SWIFT_ENABLE_EXPERIMENTAL_CXX_INTEROP:BOOL', 'TRUE')
         self.cmake_options.define('SWIFT_ENABLE_SYNCHRONIZATION:BOOL', 'TRUE')
+        self.cmake_options.define('SWIFT_ENABLE_EXPERIMENTAL_OBSERVATION:BOOL', 'TRUE')
 
         self.add_extra_cmake_options()