Fix async backend selection for Emscripten and wasm64 (#25042)

Found this while building IREE's WebGPU runtime with Emscripten for
wasm32 and wasm64 to run MLIR programs in JupyterLite.

IREE_ARCH is empty for Emscripten, so the generated CMake condition
selects POSIX. Update the converter and regenerate the async CMake file
to recognize Emscripten and wasm64.

Signed-off-by: anutosh491 <andersonbhat491@gmail.com>

build_tools/bazel/BUILD.bazel

diff --git a/build_tools/bazel/BUILD.bazel b/build_tools/bazel/BUILD.bazel
index afffddd..2518532 100644
--- a/build_tools/bazel/BUILD.bazel
+++ b/build_tools/bazel/BUILD.bazel
@@ -4,6 +4,7 @@
 # See https://llvm.org/LICENSE.txt for license information.
 # SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
+load("@bazel_skylib//lib:selects.bzl", "selects")
 load("@bazel_skylib//rules:common_settings.bzl", "string_flag")
 
 package(
@@ -75,10 +76,29 @@
 )
 
 config_setting(
-    name = "iree_is_wasm",
+    name = "iree_is_wasm32",
     constraint_values = ["@platforms//cpu:wasm32"],
 )
 
+config_setting(
+    name = "iree_is_wasm64",
+    constraint_values = ["@platforms//cpu:wasm64"],
+)
+
+config_setting(
+    name = "iree_is_emscripten",
+    constraint_values = ["@platforms//os:emscripten"],
+)
+
+selects.config_setting_group(
+    name = "iree_is_wasm",
+    match_any = [
+        ":iree_is_wasm32",
+        ":iree_is_wasm64",
+        ":iree_is_emscripten",
+    ],
+)
+
 # Selects a user-provided system allocator. Users must provide
 # IREE_ALLOCATOR_SYSTEM_CTL, and optionally IREE_ALLOCATOR_SYSTEM_SELF, via
 # their own copts/defines and link the implementation into final binaries.

build_tools/bazel_to_cmake/bazel_to_cmake_converter.py

diff --git a/build_tools/bazel_to_cmake/bazel_to_cmake_converter.py b/build_tools/bazel_to_cmake/bazel_to_cmake_converter.py
index 7c91884..31e0e1d 100644
--- a/build_tools/bazel_to_cmake/bazel_to_cmake_converter.py
+++ b/build_tools/bazel_to_cmake/bazel_to_cmake_converter.py
@@ -169,7 +169,10 @@
     def _convert_platform_condition(self, constraint_label):
         """Returns a CMake condition string for a platform constraint label."""
         if constraint_label == "//build_tools/bazel:iree_is_wasm":
-            return 'IREE_ARCH STREQUAL "wasm_32"'
+            return (
+                'EMSCRIPTEN OR IREE_ARCH STREQUAL "wasm_32" '
+                'OR IREE_ARCH STREQUAL "wasm_64"'
+            )
         cmake_name = _PLATFORM_CMAKE_SYSTEM_NAME.get(constraint_label)
         if not cmake_name:
             return None

runtime/src/iree/async/CMakeLists.txt

diff --git a/runtime/src/iree/async/CMakeLists.txt b/runtime/src/iree/async/CMakeLists.txt
index 309440e..87d5d3d 100644
--- a/runtime/src/iree/async/CMakeLists.txt
+++ b/runtime/src/iree/async/CMakeLists.txt
@@ -100,7 +100,7 @@
   list(APPEND _platform_platform_deps iree::async::platform::posix)
 elseif(CMAKE_SYSTEM_NAME STREQUAL "Windows")
   list(APPEND _platform_platform_deps iree::async::platform::iocp)
-elseif(IREE_ARCH STREQUAL "wasm_32")
+elseif(EMSCRIPTEN OR IREE_ARCH STREQUAL "wasm_32" OR IREE_ARCH STREQUAL "wasm_64")
   list(APPEND _platform_platform_deps iree::async::platform::js::proactor)
 elseif(CMAKE_SYSTEM_NAME STREQUAL "Generic")
 else()