Add NoReturn to execv* family of functions (#2226)

Author: asottile

stdlib/2/os/__init__.pyi

@@ -253,10 +253,10 @@ def execlpe(file: _PathType, __arg0: Union[bytes, Text], *args: Any) -> NoReturn
 # The docs say `args: tuple or list of strings`
 # The implementation enforces tuple or list so we can't use Sequence.
 _ExecVArgs = Union[Tuple[Union[bytes, Text], ...], List[bytes], List[Text], List[Union[bytes, Text]]]
-def execv(path: _PathType, args: _ExecVArgs) -> None: ...
-def execve(path: _PathType, args: _ExecVArgs, env: Mapping[str, str]) -> None: ...
-def execvp(file: _PathType, args: _ExecVArgs) -> None: ...
-def execvpe(file: _PathType, args: _ExecVArgs, env: Mapping[str, str]) -> None: ...
+def execv(path: _PathType, args: _ExecVArgs) -> NoReturn: ...
+def execve(path: _PathType, args: _ExecVArgs, env: Mapping[str, str]) -> NoReturn: ...
+def execvp(file: _PathType, args: _ExecVArgs) -> NoReturn: ...
+def execvpe(file: _PathType, args: _ExecVArgs, env: Mapping[str, str]) -> NoReturn: ...
 
 def _exit(n: int) -> NoReturn: ...
 def fork() -> int: ...  # Unix only

stdlib/3/os/__init__.pyi

@@ -547,10 +547,10 @@ def execlpe(file: _PathType, __arg0: Union[bytes, Text], *args: Any) -> NoReturn
 # The docs say `args: tuple or list of strings`
 # The implementation enforces tuple or list so we can't use Sequence.
 _ExecVArgs = Union[Tuple[Union[bytes, Text], ...], List[bytes], List[Text], List[Union[bytes, Text]]]
-def execv(path: _PathType, args: _ExecVArgs) -> None: ...
-def execve(path: _FdOrPathType, args: _ExecVArgs, env: Mapping[str, str]) -> None: ...
-def execvp(file: _PathType, args: _ExecVArgs) -> None: ...
-def execvpe(file: _PathType, args: _ExecVArgs, env: Mapping[str, str]) -> None: ...
+def execv(path: _PathType, args: _ExecVArgs) -> NoReturn: ...
+def execve(path: _FdOrPathType, args: _ExecVArgs, env: Mapping[str, str]) -> NoReturn: ...
+def execvp(file: _PathType, args: _ExecVArgs) -> NoReturn: ...
+def execvpe(file: _PathType, args: _ExecVArgs, env: Mapping[str, str]) -> NoReturn: ...
 
 def _exit(n: int) -> NoReturn: ...
 def fork() -> int: ...  # Unix only