Use /usr/bin/env in shebangs

Stop assuming that bash is in /bin, and that perl and python are in
/usr/bin, etc.
Instead, use env command to find these commands in the path.

tools/analyzesize.py

@@ -1,4 +1,4 @@
-#! /usr/bin/python3
+#! /usr/bin/env python3
 
 import json
 import subprocess