fix: use current python interpreter for tools

This change patches the shebang line in the tool scripts to use the
current Python interpeter. This fixes the build if either the $PATH
contains different python3 interpreter (or does not contain at all)
or /usr/bin/env is not available (e.g. Nix sandbox on macOS).

pylib/gyp/common.py

@@ -533,6 +533,10 @@ def CopyTool(flavor, out_path, generator_flags={}):
     with open(source_path) as source_file:
         source = source_file.readlines()
 
+    # Replace hash bang line with an absolute path to the Python interpreter.
+    # Note that we use shebang instead of source[0] in the output.
+    shebang = "#!" + sys.executable + "\n"
+
     # Set custom header flags.
     header = "# Generated by gyp. Do not edit.\n"
     mac_toolchain_dir = generator_flags.get("mac_toolchain_dir", None)
@@ -542,7 +546,7 @@ def CopyTool(flavor, out_path, generator_flags={}):
     # Add header and write it out.
     tool_path = os.path.join(out_path, "gyp-%s-tool" % prefix)
     with open(tool_path, "w") as tool_file:
-        tool_file.write("".join([source[0], header] + source[1:]))
+        tool_file.write("".join([shebang, header] + source[1:]))
 
     # Make file executable.
     os.chmod(tool_path, 0o755)