[tsgen] Preserve user ENVIRONMENT during TS generation. (#26049)

During TS generation we forced the environment to node only which
doesn't work with some preprocessor guards, such as in libworkerfs.js.
Instead of forcing node only, append node so the guards still pass.

Fixes #26046

Author: brendandahl

test/test_other.py

@@ -3590,6 +3590,7 @@ def test_embind_tsgen_end_to_end(self, opts, tsc_opts):
     '3': [['-sWASM=0'], 'embind_tsgen_ignore_3.d.ts'],
     '4': [['-fsanitize=undefined', '-gsource-map'], 'embind_tsgen_ignore_3.d.ts'],
     '5': [['-sASYNCIFY'], 'embind_tsgen_ignore_3.d.ts'],
+    '6': [['-sENVIRONMENT=worker', '-lworkerfs.js'], 'embind_tsgen.d.ts'],
   })
   def test_embind_tsgen_ignore(self, extra_args, expected_ts_file):
     create_file('fail.js', 'assert(false);')

tools/link.py

@@ -2011,7 +2011,8 @@ def run_embind_gen(options, wasm_target, js_syms, extra_settings):
   settings.PRE_JS_FILES = []
   settings.POST_JS_FILES = []
   # Force node since that is where the tool runs.
-  settings.ENVIRONMENT = ['node']
+  if 'node' not in settings.ENVIRONMENT:
+    settings.ENVIRONMENT.append('node')
   settings.MINIMAL_RUNTIME = 0
   # Required function to trigger TS generation.
   settings.DEFAULT_LIBRARY_FUNCS_TO_INCLUDE += ['$callRuntimeCallbacks', '$addRunDependency', '$removeRunDependency']