Minor tweak to subprocess error message.

Author: freakboy3742

.gitignore

@@ -8,4 +8,8 @@ diff/*
 dist/*
 .envrc
 .vscode/
-local/*
+local/*
+*.dist-info
+__pycache__
+tests/testbed/iOS
+tests/testbed/macOS

patch/Python/Python.patch

@@ -723,7 +723,7 @@ index 66a16a6839..dd6444892d 100644
                                  + _CASE_INSENSITIVE_PLATFORMS_STR_KEY)
 
 diff --git a/Lib/os.py b/Lib/os.py
-index 9853e37c61..7d569e55d5 100644
+index 9853e37c61..cabea71cca 100644
 --- a/Lib/os.py
 +++ b/Lib/os.py
 @@ -34,7 +34,7 @@
@@ -740,7 +740,7 @@ index 9853e37c61..7d569e55d5 100644
  del _fscodec
 
 +
-+if sys.platform in ('iOS', 'tvos', 'watchos'):
++if sys.platform in ('ios', 'tvos', 'watchos'):
 +    allows_subprocesses = False
 +else:
 +    allows_subprocesses = True
@@ -11421,15 +11421,15 @@ index 878658827c..0bc557f9e0 100644
      return f'{userbase}/lib/python{version[0]}.{version[1]}/site-packages'
 
 diff --git a/Lib/subprocess.py b/Lib/subprocess.py
-index 3f99be551c..447fd60f35 100644
+index 3f99be551c..6a4ad34d5c 100644
 --- a/Lib/subprocess.py
 +++ b/Lib/subprocess.py
 @@ -686,6 +686,9 @@
                   restore_signals=True, start_new_session=False,
                   pass_fds=(), *, encoding=None, errors=None, text=None):
          """Create new Popen instance."""
 +        if not os.allows_subprocesses:
-+            raise RuntimeError("Subprocesses are not supported on this platform.")
++            raise RuntimeError(f"Subprocesses are not supported on {sys.platform}")
 +
          _cleanup()
          # Held while anything is calling waitpid before returncode has been