Add support for -no-pthread (#20723)

Fixes: #20720

Author: sbc100

emcc.py

@@ -3747,6 +3747,10 @@ def consume_arg_file():
       settings.PTHREADS = 1
       # Also set the legacy setting name, in case use JS code depends on it.
       settings.USE_PTHREADS = 1
+    elif arg == '-no-pthread':
+      settings.PTHREADS = 0
+      # Also set the legacy setting name, in case use JS code depends on it.
+      settings.USE_PTHREADS = 0
     elif arg == '-pthreads':
       exit_with_error('unrecognized command-line option `-pthreads`; did you mean `-pthread`?')
     elif arg in ('-fno-diagnostics-color', '-fdiagnostics-color=never'):

test/test_other.py

@@ -14159,3 +14159,8 @@ def test_embind_no_duplicate_symbols(self):
     create_file('a.cpp', '#include <emscripten/bind.h>')
     create_file('b.cpp', '#include <emscripten/bind.h>')
     self.run_process([EMXX, '-std=c++23', '-lembind', 'a.cpp', 'b.cpp'])
+
+  def test_no_pthread(self):
+    self.do_runf('hello_world.c', emcc_args=['-pthread', '-no-pthread'])
+    self.assertExists('hello_world.js')
+    self.assertNotExists('hello_world.worker.js')