Update emscripten config settings to conform to the official emscripten toolchain.

Current Bazel config settings for Emscripten are specific to TensorFlow.js's custom Emscripten toolchain, but TFJS is switching to the official toolchain in [#4769](https://github.com/tensorflow/tfjs/pull/4769). The official emscripten toolchain expects `crosstool_top` to be `//emscripten_toolchain:everything`.

PiperOrigin-RevId: 360787196
diff --git a/BUILD.bazel b/BUILD.bazel
index 363a821..b1b8d01 100644
--- a/BUILD.bazel
+++ b/BUILD.bazel
@@ -7438,13 +7438,13 @@
 
 config_setting(
     name = "emscripten",
-    values = {"crosstool_top": "//toolchain:emscripten"},
+    values = {"crosstool_top": "//emscripten_toolchain:everything"},
 )
 
 config_setting(
     name = "emscripten_wasm",
     values = {
-        "crosstool_top": "//toolchain:emscripten",
+        "crosstool_top": "//emscripten_toolchain:everything",
         "cpu": "wasm",
     },
 )
@@ -7452,7 +7452,7 @@
 config_setting(
     name = "emscripten_wasmsimd",
     values = {
-        "crosstool_top": "//toolchain:emscripten",
+        "crosstool_top": "//emscripten_toolchain:everything",
         "cpu": "wasm",
         "copt": "-msimd128",
     },