Implement --print-prog-name. NFC (#25547)

Also unify with `-print-resource-dir` since they both just exec clang.

I would like to do the same with `-print-resource-dir` but sadly the
clang defaults for search dirs don't match ours just yet.

See #1610

Author: sbc100

emcc.py

@@ -250,10 +250,6 @@ def run(args):
     print(f'libraries: ={cache.get_lib_dir(absolute=True)}')
     return 0
 
-  if '-print-resource-dir' in args:
-    shared.check_call([clang] + args)
-    return 0
-
   if '-print-libgcc-file-name' in args or '--print-libgcc-file-name' in args:
     settings.limit_settings(None)
     compiler_rt = system_libs.Library.get_usable_variations()['libcompiler_rt']
@@ -292,6 +288,10 @@ def run(args):
 
   phase_setup(options, state)
 
+  if '-print-resource-dir' in args or any(a.startswith('--print-prog-name') for a in args):
+    shared.exec_process([clang] + compile.get_cflags(tuple(args)) + args)
+    assert False, 'exec_process should not return'
+
   if '--cflags' in args:
     # Just print the flags we pass to clang and exit.  We need to do this after
     # phase_setup because the setup sets things like SUPPORT_LONGJMP.
@@ -513,7 +513,7 @@ def get_clang_command_asm():
     else:
       cmd = get_clang_command() + newargs
     shared.exec_process(cmd)
-    assert False, 'exec_process does not return'
+    assert False, 'exec_process should not return'
 
   # In COMPILE_AND_LINK we need to compile source files too, but we also need to
   # filter out the link flags

test/test_other.py

@@ -751,6 +751,14 @@ def test_print_resource_dir(self):
     llvm_root = os.path.normcase(os.path.dirname(config.LLVM_ROOT))
     self.assertContained(llvm_root, resource_dir)
 
+  @crossplatform
+  def test_print_prog_name(self):
+    output = self.run_process([EMCC, '--print-prog-name=clang'], stdout=PIPE).stdout
+    expected = CLANG_CC
+    if WINDOWS:
+      expected = os.path.normpath(shared.unsuffixed(CLANG_CC))
+    self.assertContained(expected, output)
+
   @crossplatform
   @parameterized({
     '': [[]],