Rollup merge of rust-lang#74968 - lzutao:no-args, r=Mark-Simulacrum

Run all tests if have no specified tests

The behaviour was changed in rust-lang#74905 (comment)
cc @alex if you could check it again, thank you.

Author: JohnTitor

src/etc/test-float-parse/runtests.py

@@ -193,10 +193,12 @@ def interact(proc, queue):
 
 def main():
     global MAILBOX
-    tests = [os.path.splitext(f)[0] for f in glob('*.rs')
-                                    if not f.startswith('_')]
+    all_tests = [os.path.splitext(f)[0] for f in glob('*.rs') if not f.startswith('_')]
     args = sys.argv[1:]
-    tests = [test for test in tests if test in args]
+    if args:
+        tests = [test for test in all_tests if test in args]
+    else
+        tests = all_tests
     if not tests:
         print("Error: No tests to run")
         sys.exit(1)