linux uses convention of python3, bsd, notably freebsd uses python3.9 or

whatever pythons you have installed to use. extract_assets.py hardcodes
python for subsequent scripts based on linux convention, this change pulls
from environment setting of PYTHON to use that instead to allow setting in
main Makefile or environment variable for cleaner portability

extract_assets.py

@@ -3,6 +3,8 @@ import sys
 import os
 import json
 
+#respect make setting PYTHON to use, instead of assuming linux convention
+PYTHON_BIN=os.getenv('PYTHON')
 
 def read_asset_map():
     with open("assets.json") as f:
@@ -170,7 +172,7 @@ def main():
         if mio0 == "@sound":
             rom = roms[lang]
             args = [
-                "python3",
+                PYTHON_BIN,
                 "tools/disassemble_sound.py",
                 "baserom." + lang + ".z64",
             ]