build: Convert git_sha1_gen script to Python.

Python is the scripting language we've been using for scripts that need
to run across all supported platforms.

Shell is *not* a portable language for scripts.

Reviewed-by: Eric Engestrom <eric.engestrom@imgtec.com>

src/SConscript

@@ -1,6 +1,7 @@
 import filecmp
 import os
 import subprocess
+from sys import executable as python_cmd
 
 Import('*')
 
@@ -25,7 +26,7 @@ def write_git_sha1_h_file(filename):
 
     tempfile = "git_sha1.h.tmp"
     with open(tempfile, "w") as f:
-        args = [ 'sh', Dir('#').abspath + '/bin/git_sha1_gen.sh' ]
+        args = [ python_cmd, Dir('#').abspath + '/bin/git_sha1_gen.py' ]
         try:
             subprocess.Popen(args, stdout=f).wait()
         except: