bpo-30705: Fix test_regrtest.test_crashed() (#2439)

* Add test.support._crash_python() which triggers a crash but uses
  test.support.SuppressCrashReport() to prevent a crash report from
  popping up.
* Modify test_child_terminated_in_stopped_state() of test_subprocess
  and test_crashed() of test_regrtest to use _crash_python().
diff --git a/Lib/test/test_subprocess.py b/Lib/test/test_subprocess.py
index e0eb6f2..7763337 100644
--- a/Lib/test/test_subprocess.py
+++ b/Lib/test/test_subprocess.py
@@ -1277,7 +1277,7 @@
 
         code = textwrap.dedent("""
              import ctypes
-             from test.support import SuppressCrashReport
+             from test.support import _crash_python
 
              libc = ctypes.CDLL({libc_name!r})
              libc.ptrace({PTRACE_TRACEME}, 0, 0)
@@ -1288,9 +1288,8 @@
             raise unittest.SkipTest('ptrace() failed - unable to test')
 
         code += textwrap.dedent("""
-             with SuppressCrashReport():
-                # Crash the process
-                libc.printf(ctypes.c_char_p(0xdeadbeef))  # Crash the process.
+             # Crash the process
+             _crash_python()
         """)
         child = subprocess.Popen([sys.executable, '-c', code])
         try: