Cleanup test_compile a bit

setup.py

@@ -240,18 +240,15 @@ def test_compile(
 ) -> bool:
     src = src or 'int main(void) { return 0; }'
     with tempfile.TemporaryDirectory(prefix='kitty-test-compile-') as tdir:
+        with open(os.path.join(tdir, f'source.{lang}'), 'w', encoding='utf-8') as srcf:
+            print(src, file=srcf)
         p = subprocess.Popen(
-            [cc] + list(cflags) + ([] if link_also else ['-c']) + ['-x', lang, '-o', os.path.join(tdir, 'dummy'), '-'] +
+            [cc] + list(cflags) + ([] if link_also else ['-c']) +
+            ['-o', os.path.join(tdir, 'source.output'), srcf.name] +
             [f'-l{x}' for x in libraries] + list(ldflags),
-            stdout=subprocess.DEVNULL, stdin=subprocess.PIPE, stderr=None if show_stderr else subprocess.DEVNULL
+            stdout=subprocess.DEVNULL, stdin=subprocess.DEVNULL,
+            stderr=None if show_stderr else subprocess.DEVNULL
         )
-        stdin = p.stdin
-        assert stdin is not None
-        try:
-            stdin.write((src + '\n').encode('utf-8'))
-            stdin.close()
-        except BrokenPipeError:
-            return False
         return p.wait() == 0