Remove check for file type of .a files. NFC (#21513)

Instead just pass them through the linker like other inputs.

See #21128

emcc.py

@@ -39,7 +39,7 @@
 from tools.shared import unsuffixed, unsuffixed_basename, get_file_suffix
 from tools.shared import run_process, exit_with_error, DEBUG
 from tools.shared import in_temp, OFormat
-from tools.shared import DYNAMICLIB_ENDINGS, STATICLIB_ENDINGS
+from tools.shared import DYNAMICLIB_ENDINGS
 from tools.response_file import substitute_response_files
 from tools import config
 from tools import cache
@@ -755,12 +755,6 @@ def phase_setup(options, state, newargs):
       file_suffix = get_file_suffix(arg)
       if file_suffix in HEADER_ENDINGS:
         has_header_inputs = True
-      if file_suffix in STATICLIB_ENDINGS and not building.is_ar(arg):
-        if building.is_bitcode(arg):
-          message = f'{arg}: File has a suffix of a static library {STATICLIB_ENDINGS}, but instead is an LLVM bitcode file! When linking LLVM bitcode files use .bc or .o.'
-        else:
-          message = arg + ': Unknown format, not a static library!'
-        exit_with_error(message)
       input_files.append((i, arg))
     elif arg.startswith('-L'):
       state.add_link_flag(i, arg)

test/test_other.py

@@ -512,6 +512,10 @@ def test_bc_output_warning(self):
     err = self.run_process([EMCC, '-c', test_file('hello_world.c'), '-o', 'out.bc'], stderr=PIPE).stderr
     self.assertContained('emcc: warning: .bc output file suffix used without -flto or -emit-llvm', err)
 
+  def test_bc_as_archive(self):
+    self.run_process([EMCC, '-c', test_file('hello_world.c'), '-flto', '-o', 'out.a'])
+    self.run_process([EMCC, 'out.a'])
+
   @parameterized({
     'c': [EMCC, '.c'],
     'cxx': [EMXX, '.cpp']