Convert Python scripts to Python 3

Change all of the #! lines in Python scripts that are called from
Makefiles to reference /usr/bin/python3.

All of the scripts called from Makefiles are already run with Python 3,
so let's make sure they are explicitly using Python 3 if called
manually.

benchtests/scripts/bench.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/python3
 # Copyright (C) 2014-2020 Free Software Foundation, Inc.
 # This file is part of the GNU C Library.
 #

benchtests/scripts/validate_benchout.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/python3
 # Copyright (C) 2014-2020 Free Software Foundation, Inc.
 # This file is part of the GNU C Library.
 #

conform/glibcconform.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/python3
 # Shared code for glibc conformance tests.
 # Copyright (C) 2018-2020 Free Software Foundation, Inc.
 # This file is part of the GNU C Library.

conform/linknamespace.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/python3
 # Check that use of symbols declared in a given header does not result
 # in any symbols being brought in that are not reserved with external
 # linkage for the given standard.

conform/list-header-symbols.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/python3
 # Print a list of symbols exported by some headers that would
 # otherwise be in the user's namespace.
 # Copyright (C) 2018-2020 Free Software Foundation, Inc.

math/gen-libm-test.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/python3
 # Generate tests for libm functions.
 # Copyright (C) 2018-2020 Free Software Foundation, Inc.
 # This file is part of the GNU C Library.

math/gen-tgmath-tests.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/python3
 # Generate tests for <tgmath.h> macros.
 # Copyright (C) 2017-2020 Free Software Foundation, Inc.
 # This file is part of the GNU C Library.