buildsys: move file regeneration logic to the script itself

Signed-off-by: Eric Engestrom <eric.engestrom@imgtec.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Dylan Baker <dylan@pnwbakers.com>

src/SConscript

@@ -24,22 +24,12 @@ def write_git_sha1_h_file(filename):
     to retrieve the git hashid and write the header file.  An empty file
     will be created if anything goes wrong."""
 
-    tempfile = "git_sha1.h.tmp"
-    with open(tempfile, "w") as f:
-        args = [ python_cmd, Dir('#').abspath + '/bin/git_sha1_gen.py' ]
-        try:
-            subprocess.Popen(args, stdout=f).wait()
-        except:
-            print("Warning: exception in write_git_sha1_h_file()")
-            return
-
-    if not os.path.exists(filename) or not filecmp.cmp(tempfile, filename):
-        # The filename does not exist or it's different from the new file,
-        # so replace old file with new.
-        if os.path.exists(filename):
-            os.remove(filename)
-        os.rename(tempfile, filename)
-    return
+    args = [ python_cmd, Dir('#').abspath + '/bin/git_sha1_gen.py', '--output', filename ]
+    try:
+        subprocess.call(args)
+    except:
+        print("Warning: exception in write_git_sha1_h_file()")
+        return
 
 
 # Create the git_sha1.h header file