Use env to invoke python

/usr/bin/python may be python3. We should respect PATH to find the python
executable so it can be locally overridden to be python2.

Test: Build libc, repo upload
Change-Id: Iaddd7cd4a1c2177c32786e4fa0fc664ab0ad36de

libc/kernel/tools/cpp.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/env python
 """A glorified C pre-processor parser."""
 
 import ctypes

libc/tools/check-symbols.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/env python
 
 import glob
 import os

libc/tools/generate-NOTICE.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/env python
 # Run with directory arguments from any directory, with no special setup required.
 # Or:
 # for i in libc libdl libm linker libstdc++ ; do ./libc/tools/generate-NOTICE.py $i > $i/NOTICE ; done

libc/tools/gensyscalls.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/env python
 
 # This tool is used to generate the assembler system call stubs,
 # the header files listing all available system calls, and the

libc/tools/genversion-scripts.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/env python
 
 # This tool is used to generate the version scripts for libc and libm
 # for every architecture.