Close the temporary file before using it

An instance of NamedTemporaryFile would keep the file open in the
current process, however, on Windows, a opened filed is no accessible
from any other process, and thus the following commands use this file
would fail to execute.

To fix this, this commit ensures that the temporary file has been closed
before it is used anywhere else, and removes the temporary file after
everything gets done.

ports/geckolib/gecko_bindings/tools/regen.py

@@ -284,10 +284,11 @@ def build(objdir, target_name, kind_name=None,
         print("[RUSTC]... ", end='')
         sys.stdout.flush()
 
-        tests_file = tempfile.NamedTemporaryFile()
+        with tempfile.NamedTemporaryFile(delete=False) as f:
+            test_file = f.name
         output = None
         try:
-            rustc_command = ["rustc", output_filename, "--test", "-o", tests_file.name]
+            rustc_command = ["rustc", output_filename, "--test", "-o", test_file]
             output = subprocess.check_output(rustc_command, stderr=subprocess.STDOUT)
             output = output.decode('utf8')
         except subprocess.CalledProcessError as e:
@@ -299,17 +300,17 @@ def build(objdir, target_name, kind_name=None,
         if verbose:
             print(output)
 
-        tests_file.file.close()
         print("[RUSTC_TEST]... ", end='')
         sys.stdout.flush()
 
         try:
-            output = subprocess.check_output([tests_file.name], stderr=subprocess.STDOUT)
+            output = subprocess.check_output([test_file], stderr=subprocess.STDOUT)
             output = output.decode('utf8')
         except subprocess.CalledProcessError as e:
             print("tests failed: ", e.output.decode('utf8'))
             return 1
 
+        os.remove(test_file)
         print("OK")
 
         # TODO: this -3 is hacky as heck