scan-build-py: fix multiprocessing error

[lawrence_danna]

Summary

Recent versions of python3's multiprocessing module will blow up with
a Runtime error from this code, saying:

An attempt has been made to start a new process before the
current process has finished its bootstrapping phase

This is becuae the wrappers in bin/ are not using the __name__ == "__main__" idiom correctly.

[ldionne]

From the docs:

multiprocessing.freeze_support()
Add support for when a program which uses multiprocessing has been frozen to produce a Windows executable. (Has been tested with py2exe, PyInstaller and cx_Freeze.)

One needs to call this function straight after the if __name__ == '__main__' line of the main module. For example: [...]

So this looks right to me, but I'm not a Clang owner.

clang/tools/scan-build-py/bin/analyze-build

 #!/usr/bin/env python
 # -*- coding: utf-8 -*-
 # Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 # See https://llvm.org/LICENSE.txt for license information.
 # SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 import multiprocessing
-multiprocessing.freeze_support()
-
 import sys
 import os.path
 this_dir = os.path.dirname(os.path.realpath(__file__))
 sys.path.append(os.path.dirname(this_dir))
 
 from libscanbuild.analyze import analyze_build
+
+if __name__ == '__main__':
+    multiprocessing.freeze_support()
     sys.exit(analyze_build())

clang/tools/scan-build-py/bin/intercept-build

 #!/usr/bin/env python
 # -*- coding: utf-8 -*-
 # Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 # See https://llvm.org/LICENSE.txt for license information.
 # SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 import multiprocessing
-multiprocessing.freeze_support()
-
 import sys
 import os.path
 this_dir = os.path.dirname(os.path.realpath(__file__))
 sys.path.append(os.path.dirname(this_dir))
 
 from libscanbuild.intercept import intercept_build
+
+if __name__ == '__main__':
+    multiprocessing.freeze_support()
     sys.exit(intercept_build())

clang/tools/scan-build-py/bin/scan-build

 #!/usr/bin/env python
 # -*- coding: utf-8 -*-
 # Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 # See https://llvm.org/LICENSE.txt for license information.
 # SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 import multiprocessing
-multiprocessing.freeze_support()
-
 import sys
 import os.path
 this_dir = os.path.dirname(os.path.realpath(__file__))
 sys.path.append(os.path.dirname(this_dir))
 
 from libscanbuild.analyze import scan_build
+
+if __name__ == '__main__':
+    multiprocessing.freeze_support()
     sys.exit(scan_build())