Allow using the search path from -resource-dir with emcc -print-file-name (#27082)

This allows emcc to change the search path when running it like: `emcc
-resource-dir=... -print-file-name=...` which mimics the upstream clang
behavior.

Author: Diyou

emcc.py

@@ -265,7 +265,11 @@ def main(args):
   print_file_name = [a for a in args if a.startswith(('-print-file-name=', '--print-file-name='))]
   if print_file_name:
     libname = print_file_name[-1].split('=')[1]
-    system_libpath = cache.get_lib_dir(absolute=True)
+    resource_dir = [a for a in args if a.startswith(('-resource-dir=', '--resource-dir='))]
+    if resource_dir:
+      system_libpath = resource_dir[-1].split('=')[1]
+    else:
+      system_libpath = cache.get_lib_dir(absolute=True)
     fullpath = os.path.join(system_libpath, libname)
     if os.path.isfile(fullpath):
       print(fullpath)

test/test_other.py

@@ -776,6 +776,14 @@ def test_print_file_name(self, args):
     settings.MEMORY64 = int('-m64' in args)
     self.assertContained(cache.get_lib_name('libc.a'), str(filename))
 
+  @crossplatform
+  def test_print_file_name_with_resource_dir(self):
+    file = Path(EMCC).name
+    output = self.run_process([EMCC, f'-print-file-name={file}'], stdout=PIPE).stdout
+    output_relative = self.run_process([EMCC, '-resource-dir=' + path_from_root(), f'-print-file-name={file}'], stdout=PIPE).stdout
+    self.assertNotExists(output.rstrip())
+    self.assertExists(output_relative.rstrip())
+
   def test_emar_em_config_flag(self):
     # Test that the --em-config flag is accepted but not passed down do llvm-ar.
     # We expand this in case the EM_CONFIG is ~/.emscripten (default)