Use the same Python executable instead of `python`

`python` might be the wrong version, for example it might be Python 2 on
some systems, or it might be a different version of Python 3. Use
`sys.executable`, so that the same version gets used consistently.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

scripts/make_generated_files.py

diff --git a/scripts/make_generated_files.py b/scripts/make_generated_files.py
index 73570fb..5658799 100755
--- a/scripts/make_generated_files.py
+++ b/scripts/make_generated_files.py
@@ -33,7 +33,7 @@
 
         # Executable to run the script, needed for Windows
         if script.suffix == ".py":
-            self.exe = "python"
+            self.exe = sys.executable
         elif script.suffix == ".pl":
             self.exe = "perl"
 
@@ -62,7 +62,7 @@
     """
     files = []
     if generation_script.endswith(".py"):
-        cmd = ["python"]
+        cmd = [sys.executable]
     elif generation_script.endswith(".pl"):
         cmd = ["perl"]
     cmd += [generation_script, "--list"]