Bazel add html support (#765)

* allow the bazel toolchain to output html files

* allow for cc_binary rule names to end in .js

* fix python name

* continue to call emcc instead of em++ for now

* small cleanup

Co-authored-by: Mitch Foley <mitchfoley@chromium.org>

bazel/emscripten_toolchain/crosstool.bzl

@@ -436,6 +436,11 @@ def _impl(ctx):
         # https://emscripten.org/docs/debugging/Sanitizers.html
         feature(name = "wasm_asan"),
         feature(name = "wasm_ubsan"),
+
+        feature(
+            name = "output_format_js",
+            enabled = True,
+        ),
     ]
 
     crosstool_default_flag_sets = [
@@ -547,6 +552,11 @@ def _impl(ctx):
             flags = ["-s", "PRINTF_LONG_DOUBLE=1"],
             features = ["precise_long_double_printf"],
         ),
+        flag_set(
+            actions = all_link_actions,
+            flags = ["--oformat=js"],
+            features = ["output_format_js"],
+        ),
 
         # Opt
         flag_set(