Here's a caroline-llvm-toolchain trybot run: https://uberchromegw.corp.google.com/i/chromiumos.tryserver/builders/llvm_toolchain/builds/200

It did not run hwtests.

The llvm_toolchain template in chromeos_config.py specifies hwtests:

  site_config.AddTemplate(
      'llvm_toolchain',
      site_config.templates.toolchain,
      description='Full release build with LLVM toolchain',
      latest_toolchain=True,
      hw_tests=hw_test_list.ToolchainTestMedium(constants.HWTEST_SUITES_POOL),
      hw_tests_override=hw_test_list.ToolchainTestMedium(
          constants.HWTEST_SUITES_POOL),
  )

Note that both hw_tests and hw_tests_override contain the same set of tests.
This is reflected in config_dump.json for llvm_toolchain template: both hw_tests and hw_tests_override contain the same tests.

If I run the same caroline-llvm-toolchain trybot with --hwtest, hwtests are run: https://uberchromegw.corp.google.com/i/chromiumos.tryserver/builders/llvm_toolchain/builds/199

The same tests should run even without passing the --hwtests flag.